ISO 6621-4:2003

Internal combustion engines — Piston rings — Part 4: General specifications

ISO 6621-4:2003 specifies the general characteristics of piston rings for both reciprocating internal combustion engines and compressors (the individual dimensional criteria for these rings are given in the relevant International Standards). It also provides a system for ring coding, designation and marking. It is applicable to all such rings of a diameter greater than or equal to 200 mm.

Moteurs à combustion interne — Segments de piston — Partie 4: Spécifications générales

General Information

• Status: Withdrawn
• Publication Date: 13-Oct-2003
• Withdrawal Date: 13-Oct-2003
• ICS: 43.060.10 - Engine block and internal components
• Technical Committee: ISO/TC 22 - Road vehicles
• Drafting Committee: ISO/TC 22 - Road vehicles
• Current Stage: 9599 - Withdrawal of International Standard
• Completion Date: 18-Mar-2015

Relations

• Revised: ISO 6621-4:2015 - Internal combustion engines — Piston rings — Part 4: General specifications
• Effective Date: 29-Jan-2011
• Revises: ISO 6621-4:1988 - Internal combustion engines — Piston rings — Part 4: General specifications
• Effective Date: 15-Apr-2008
• Consolidated By: ISO/TS 21623:2017 - Workplace exposure — Assessment of dermal exposure to nano-objects and their aggregates and agglomerates (NOAA)
• Effective Date: 06-Jun-2022

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 6621-4
Second edition
2003-10-15

Internal combustion engines — Piston
rings —
Part 4:
General specifications
Moteurs à combustion interne — Segments de piston —
Partie 4: Spécifications générales




Reference number
ISO 6621-4:2003(E)
©
ISO 2003

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ISO 6621-4:2003(E)
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ii © ISO 2003 — All rights reserved

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ISO 6621-4:2003(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Piston ring codes . 1
5 Designation of piston rings. 4
5.1 Designation elements and order . 4
5.2 Designation examples . 5
6 Marking of piston rings . 6
6.1 General. 6
6.2 Mandatory top-side marking. 7
6.3 Additional marking. 7
7 General characteristics . 7
7.1 Ring shape. 7
7.2 Light tightness . 8
7.3 Closed gap. 8
7.4 Tangential force, F , and diametral force, F , of single piece piston rings . 8
t d
7.5 Tangential force F of multipiece oil control rings as specified in ISO 6626 . 12
t
7.6 Tangential force F of expander/segment oil control rings as specified in ISO 6627 . 13
t
8 Notches for preventing ring rotation . 14
8.1 Ring joint with internal notch (only for compression rings as specified in ISO 6622 and
ISO 6624). 14
8.2 Ring joint with side notch (only for compression rings as specified in ISO 6622). 15
9 Machining of surfaces . 16
9.1 Peripheral surfaces. 16
9.2 Side faces. 16
9.3 Other surfaces. 16
10 Plated, coated and treated surfaces . 18
10.1 Chromium plating on peripheral surfaces. 18
10.2 Spray-coated peripheral surfaces . 21
10.3 Nitrided surfaces. 24
10.4 Treated surfaces . 26
11 Miscellaneous. 26
11.1 Cleanliness . 26
11.2 Corrosion protection . 26
11.3 Packaging . 27
Bibliography . 28

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ISO 6621-4:2003(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 6621-4 was prepared by Technical Committee ISO/TC 22, Road vehicles.
This second edition cancels and replaces the first edition (ISO 6621-4:1988), which has been technically
revised.
ISO 6621 consists of the following parts, under the general title Internal combustion engines — Piston rings:
 Part 1: Vocabulary
 Part 2: Inspection measuring principles
 Part 3: Material specifications
 Part 4: General specifications
 Part 5: Quality requirements
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ISO 6621-4:2003(E)
Introduction
ISO 6621 is one of a series of International Standards dealing with piston rings for reciprocating internal
[1], [2] [3] [4], [5], [6], [7] [8]
combustion engines. Others are ISO 6622 , ISO 6623 , ISO 6624 , ISO 6625 ,
[9], [10] [11]
ISO 6626 and ISO 6627 .

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INTERNATIONAL STANDARD ISO 6621-4:2003(E)

Internal combustion engines — Piston rings —
Part 4:
General specifications
1 Scope
This part of ISO 6621 specifies the general characteristics of piston rings for both reciprocating internal
combustion engines and compressors (the individual dimensional criteria for these rings are given in the
relevant International Standards). It also provides a system for ring coding, designation and marking. It is
applicable to all such rings of a diameter u 200 mm.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 6507-3, Metallic materials — Vickers hardness test — Part 3: Calibration of reference blocks
ISO 6621-1, Internal combustion engines — Piston rings — Part 1: Vocabulary
ISO 6621-2:2003, Internal combustion engines — Piston rings — Part 2: Inspection measuring principles
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 6621-1 apply.
4 Piston ring codes
Codes used for piston rings shall be as given in Table 1, corresponding to their explanatory descriptions.
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ISO 6621-4:2003(E)
Table 1 — Codes and descriptions
Code Description Relevant International
Standard
R Straight faced rectangular ring ISO 6622-1, ISO 6622-2
B Barrel faced rectangular ring ISO 6622-1, ISO 6622-2
BA Asymmetrical barrel faced rectangular ring ISO 6622-1, ISO 6622-2
M1 .M5 Taper faced rectangular ring ISO 6622-1, ISO 6622-2
N Napier ring (undercut step) ISO 6623
NM1 . NM4 Napier ring (undercut step), taper faced ISO 6623
E Scraper ring (stepped) ISO 6623
EM1 . EM4 Scraper ring (stepped), taper faced ISO 6623
T Straight faced keystone ring 6° ISO 6624-1, ISO 6624-3
TB Barrel faced keystone ring 6° ISO 6624-1, ISO 6624-3
TBA Asymmetrical barrel faced keystone ring 6° ISO 6624-1, ISO 6624-3
TM1 . TM5 Taper faced keystone ring 6° ISO 6624-1, ISO 6624-3
K Straight faced keystone ring 15° ISO 6624-1, ISO 6624-3
KB Barrel faced keystone ring 15° ISO 6624-1, ISO 6624-3
KBA Asymmetrical barrel faced keystone ring 15° ISO 6624-1, ISO 6624-3
KM1 . KM5 Taper faced keystone ring 15° ISO 6624-1, ISO 6624-3
HK Straight faced half keystone ring 7° ISO 6624-2, ISO 6624-4
HKB Barrel faced half keystone ring 7° ISO 6624-2, ISO 6624-4
S Slotted oil control ring ISO 6625
G Double bevelled oil control ring ISO 6625
D Bevelled edge oil control ring ISO 6625
DV Bevelled edge V-groove oil control ring ISO 6625
DSF-C Coil spring loaded bevelled edge oil control ring, chromium
ISO 6626, ISO 6626-2
plated and profile ground
DSF-CNP Coil spring loaded bevelled edge oil control ring, chromium
ISO 6626
plated, not profile ground
SSF Coil spring loaded slotted oil control ring ISO 6626, ISO 6626-2
GSF Coil spring loaded double bevelled oil control ring ISO 6626, ISO 6626-2
DSF Coil spring loaded bevelled edge oil control ring ISO 6626, ISO 6626-2
DSF-NG Coil spring loaded bevelled edge oil control ring(face geometry
ISO 6626
similar type DSF-C or DSF-CNP)
SSF-L Coil spring loaded slotted oil control ring with 0,6 mm nominal
ISO 6626, ISO 6626-2
land width
ES-1 . ES-4 Expander/ segment oil control rings ISO 6627
D22 Radial wall thickness for “D/22” ISO 6622-1, ISO 6623
MC11 . MC68 Material subclasses ISO 6621-3
MR Ratio m/(d −a ) reduced ISO 6621-4
1 1
Z Ring shape round ISO 6621-4

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ISO 6621-4:2003(E)
Table 1 (continued)
Code Description Relevant International
Standard
Y Ring shape negative ovality ISO 6621-4
S005 . S100 Closed gap (minimum values) ISO 6621-4
CRF . CR4 Peripheral surface chromium plated fully faced design ISO 6621-4
CR1E . CR2E Peripheral surface chromium plated semi-inlaid design ISO 6621-4
CR1F . CR2F Peripheral surface chromium plated inlaid design ISO 6621-4
SC1 . SC4 Peripheral surface spray coated fully faced design ISO 6621-4
SC1E . SC4E Peripheral surface spray coated semi-inlaid design ISO 6621-4
SC1F . SC4F Peripheral surface spray coated inlaid design ISO 6621-4
NT030 . NT130 Nitrided surface, case depth specified on peripheral surface ISO 6621-4
and side faces
NB030 . NB130 Nitrided surface, case depth specified on peripheral surface ISO 6621-4
and bottom side
NP030 . NP130 Nitrided surface, case depth specified on peripheral surface ISO 6621-4
only
NS010 . NS050 Nitrided surface, case depth on segments ISO 6627
NX Nitrided surface of expanders/spacers ISO 6627
LF Uncoated ring peripheral surface or uncoated land peripheral ISO 6621-4
surface, fully lapped
LP Taper faced piston ring with lapped land over the whole ISO 6621-4
circumference but not over the whole width of the peripheral
surface
LM Taper faced piston ring with partly cylindrical machined ISO 6621-4
peripheral surface
FE Ferro oxided on all sides ISO 6621-4
PO Phosphated on all sides ISO 6621-4
PR Phosphated on all sides (for rust protection purposes) ISO 6621-4
KA Peripheral edges chamfered ISO 6622
KI Inside edges chamfered ISO 6622
IF Internal bevel (top side) ISO 6622, ISO 6624-1, ISO 6624-3
IFU Internal bevel (bottom side) ISO 6622
IW Internal step (top side) ISO 6622-1, ISO 6624-1
IWU Internal step (bottom side) ISO 6622-1
IFV Variable internal bevel (top side) for defined twist ISO 6622-1
IFVU Variable internal bevel (bottom side) for defined twist ISO 6622-1
KU Reduced peripheral bottom edge chromium plated fully faced ISO 6621-4
design
KG Reduced size of peripheral edges at the gap of chromium ISO 6621-4
plated/ spray coated/ nitrided rings
NE1 . NE3 Ring joint with lateral stop ISO 6621-4
NH1 . NH3 Ring joint with internal stop ISO 6621-4
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ISO 6621-4:2003(E)
Table 1 (continued)
Code Description Relevant International
Standard
WK Reduced slot length ISO 6626, ISO 6626-2
WF Reduced heat set ISO 6621-5, ISO 6626, ISO 6626-2
CSN, CSG, CSE Type of coil spring ISO 6626, ISO 6626-2
PNE, PNL, PNR, Contact pressure class ISO 6626, ISO 6626-2, ISO 6627
PNM, PNH, PNV
Additional marking
MM Manufacturer's mark ISO 6621-4
MZ Mark for required ring shape “round” ISO 6621-4
MY Mark for required ring shape “negative ovality” ISO 6621-4
a
MX ISO 6621-4
Material mark

b
MU ISO 6621-4
Any other additional mark
a
Material mark (for alternative materials) at the discretion of the manufacturer.
b
Any other additional marking on client’s request, which shall be quoted clearly in the order, shall be agreed between manufacturer
and client.
5 Designation of piston rings
5.1 Designation elements and order
5.1.1 General
When designating piston rings complying with the relevant International Standards, the following details shall
be provided, in the order given, using the codes according to Table 1.
5.1.2 Mandatory elements
The following mandatory elements shall constitute the designation of a piston ring:
 designation, i.e. piston ring;
 number of International Standard;
 type of piston ring, e.g. R;
 hyphen;
 size of piston ring, d × h ;
1 1
 radial wall thickness “regular” without code;
 Code D22 if the selected wall thickness, in accordance with ISO 6622-1 and ISO 6623, is D/22;
 hyphen;
 material code, e.g. MC11.
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ISO 6621-4:2003(E)
5.1.3 Additional elements
The following optional elements may be added to the designation of a piston ring and, if so added, shall be
positioned on a second line beneath, or separated by a slash (/) from, the mandatory elements given in 5.1.2.
 reduced ratio m/(d − a ), MR;
1 1
 ring shape, e.g. Z;
 selected nominal closed gap if it differs from the closed gap specified in the dimension Tables, e.g. S05;
 the selected coating, e.g. CR3;
 uncoated rings with fully lapped peripheral surface, e.g. for LF taper faced rings with partly cylindrical
peripheral surface, LM (machined) or LP (lapped);
 selected surface treatment, e.g. PO;
 selected inside edge feature, e.g. KA;
 inside step of bevel, e.g. IWU;
 selected notch to prevent ring rotation, e.g. NH1;
 reduced slot length, if required, WK;
 coil spring with reduced heat set, if required, e.g. WF;
 selected type of coil spring, e.g. CSG;
 selected pressure class, e.g. PNM.
5.1.4 Elements for additional marking
Any additional marking shall following the additional elements of 5.1.3:
 manufacturer's mark, if required, MM;
 marking of required ring shape, e.g. MZ;
 material, MX (see Table 1, Footnote a);
 code for any other marking, MU (see Table 1, Footnote b).
5.2 Designation examples
5.2.1 Designation example of a piston ring in accordance with ISO 6622-1
For
 a straight-faced rectangular ring (R),
 of nominal diameter d = 90 mm (90),
1
 of nominal ring width h = 2,5 mm (2,5), and
1
 made of grey cast iron, non heat-treated, material subclass 11 (MC11):
Piston ring ISO 6622-1 R - 90 ×××× 2,5 - MC11
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ISO 6621-4:2003(E)
5.2.2 Designation example of a piston ring in accordance with ISO 6624-1
For
 a keystone ring 6°, taper faced 60′ (TM3),
 of nominal diameter d = 105 mm (105),
1
 and nominal ring width h = 2,5 mm (2,5),
1
 made of spheroidal graphite cast iron, martensitic type, material subclass 51 (MC51),
 ring shape round (Z),
 with a selected closed gap of 0,3 mm (S003),
 inside edges chamfered (KI), and
 peripheral surface chromium plated, with plating thickness 0,1 mm minimum (CR2):
Piston ring ISO 6624-1 TM3 - 105 ×××× 2,5 - MC51 / Z S003 KI CR2
5.2.3 Designation example of a piston ring in accordance with ISO 6626
For
 a coil spring loaded, bevelled edge oil control ring, chromium plated and profile ground (DSF-C),
 of nominal diameter d = 125 mm (125),
1
 and nominal ring width h = 5 mm (5),
1
 made of grey cast iron, non heat-treated, material subclass 11 (MC11),
 with a selected closed gap of 0,2 mm (S002),
 having a chromium plating thickness on the lands of 0,15 mm minimum (CR3),
 phosphated on all cast iron surfaces to a depth of 0,002 mm minimum (PO),
 with reduced slot length (WK),
 a coil spring with reduced heat seat (WF),
 having a variable pitch with coil diameter, d ground (CSE),
1
 tangential force F according to the medium nominal contact pressure class (PNM),
t
 marked with manufacturer's mark (MM):
Piston ring ISO 6626 DSF-C - 125 ×××× 5 - MC11 / S002 CR3 PO WK WF CSE PNM MM
6 Marking of piston rings
6.1 General
The requirements and recommendations for piston ring marking according to 6.2 and 6.3 apply to piston rings
of 1,6 mm radial wall thickness and above. Marking of piston rings of less than 1,6 mm is at the discretion of
the manufacturer.
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ISO 6621-4:2003(E)
6.2 Mandatory top-side marking
All rings requiring orientation shall be marked to indicate the top side only, i.e. the side nearest the combustion
chamber.
In the absence of any other mark agreed between manufacturer and client, the mark “TOP” should be used.
Marking of the top side applies to all the following types of ring:
 taper faced rings;
 asymmetrical barrel faced rings;
 rings with reduced peripheral bottom edge;
 internally bevelled or stepped rings;
 semi-inlaid rings;
 scraper rings;
 half keystone rings;
 directional oil control rings.
All such rings requiring marking are specified in the relevant International Standards (see Foreword and
Bibliography).
6.3 Additional marking
Additional marking of piston rings is optional or at the client's request.
Such additional marking may comprise the following:
 manufacturer's mark;
 mark for required ring shape;
 material mark (for alternative materials);
 any other additional mark agreed between manufacturer and client.
7 General characteristics
7.1 Ring shape
[1], [2] [3] [4], [5], [6], [7]
Degrees of ovality only apply to rectangular rings , scraper rings and keystone rings . The
forms of ovality are
 positive ovality, without code,
 round, Code Z, and
 negative ovality, Code Y.
Values are given in Table 2.
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ISO 6621-4:2003(E)
Table 2 — Ovality
Dimensions in millimetres

a b
Nominal diameter Positive ovality Round Negative ovality
d Code: Z Code: Y
1
30 u d < 60 0 . + 0,60 − 0,30 . + 0,30 − 0,60 . 0
1
60 u d < 100 + 0,05 . + 0,85 − 0,35 . + 0,35 − 0,70 . 0
1
100 u d < 150 + 0,10 . + 1,10 − 0,45 . + 0,45 − 0,95 . − 0,05
1
150 u d u 200 + 0,15 . + 1,35 − 0,50 . + 0,50 − 1,10 . − 0,10
1
a
For taper faced coated and uncoated rings with lapped land, the recommended ring shape is round.
b
Not applicable for material Class 10 of ISO 6621-3.
7.2 Light tightness
At least 90 % of the circumference of the piston ring peripheral surface shall be light-tight.
At least 95 % of the circumference on the peripheral surface of a taper faced ring with plated/coated or
nitrided and ground peripheral surface shall be light-tight.
100 % of the circumference on the peripheral surface of the following piston ring designs shall be light-tight:
 piston rings with machined land over the whole circumference of the peripheral surface;
 taper-faced piston rings with machined land over the whole circumference of the peripheral surface.
In the case of piston rings with a treated surface, the light tightness is normally measured prior to surface
treatment. When it is checked after treatment, rotation of the ring in the gauge will be required. In the case of
rings with negative point deflection, visible light is permitted at the butt ends, but should be confined to the
angle θ as defined in ISO 6621-2.
7.3 Closed gap
Whenever the selected closed gap differs from that given in the dimensional tables of the relevant
International Standard, Table 3 shall apply and the tolerances shall remain the same.
Table 3 — Closed gap
Dimensions in millimetres
Code S005 S010 S015 S020 S025 S030 S035 S040 S045 S050 S055 S060 S070 S080 S090 S100
Closed gap 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45 0,50 0,55 0,60 0,70 0,80 0,90 1,00
7.4 Tangential force, F , and diametral force, F , of single piece piston rings
t d
NOTE The individual types of piston rings are given in [1] to [8]. The definitions of F and F are given in ISO 6621-2.
t d
7.4.1 Calculation of F and F values in dimension tables of dimensional standards
t d
The tangential and diametral forces of piston rings are tabulated in the dimension tables of the dimensional
standards.
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ISO 6621-4:2003(E)
The values are calculated for
 the basic feature of each piston ring type,
 nominal radial wall thickness a , and mean ring width h or h ,
1 1 3

2 2
 piston rings made of cast iron with a modulus of elasticity of 100 GN/m (100 GN/m =
2
100 000 MPa = 100 000 N/mm ),
2
 piston rings made of steel with a modulus of elasticity of 210 GN/m , and
 a ratio of total free gap to nominal diameter [m/(d − a )] according to Table 4.
1 1
NOTE The calculation of tangential forces and diametral forces of rectangular rings made of steel (ISO 6622-2) is
2
based on a theoretical contact pressure of 0,16 ± 0,01 N/mm . The calculation of tangential forces and diametral forces of
keystone rings (ISO 6624-3) and half keystone rings (ISO 6624-4) made of steel is based on the same ratio m/(d − a )
1 1
used for rectangular rings (ISO 6622-2).The ratio m/(d − a ) for rings made of steel is quite different from the values given
1 1
in Table 4 for rings made of cast iron and depends on the nominal diameter and the special radial wall thickness. This
radial wall thickness is not in a constant ratio to nominal diameter because there are steps of wall thickness which belong
to a range of nominal diameters (e.g. a = 2,1 mm for d = 57 . 61 mm).
1 1
7.4.2 Correction of F and F values

t d
7.4.2.1 General
The F and F values shall be corrected whenever the following are being used:
t d
a) additional features, such as rings with
 coated peripheral surface, and/or
 inside chamfered edges, and/or
 outside chamfered edges, and/or
 taper, and/or
 internal step or internal bevel;
2
b) piston ring materials with a modulus of elasticity other than 100 GN/m ;
c) a ratio of total free gap to nominal diameter [m/(d − a )] other than that given in Table 4;
1 1
The values for the regular ratio of free gap to nominal diameter m/(d − a ) regular are given in Table 4.
1 1
Table 4 — Regular ratio of total free gap to nominal diameter
Dimensions in millimetres
m/(d − a )
Nominal diameter 1 1
a
d
Cast iron
Steel
1
30 u d < 60
1
0,15 0,10 . 0,14
60 u d < 100
1
100 u d < 160
1
0,17-0,0002 d
0,11 . 0,13
1
160 u d u 200
1
a
Variation of m/(d − a ) depends on contact pressure and radial wall thickness.
1 1
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ISO 6621-4:2003(E)
7.4.2.2 Multiplier factors for common features
For common features, the necessary multiplier correction factors are tabulated in the dimensional standards
[1] to [8] under “Force factors”.
7.4.2.3 Multiplier force correction factors for materials
For materials specified in ISO 6621-3, the force correction factors given in Table 5 should be used.
Table 5 — Material force correction factors
Material class Material force correction factor
a
10
0,9 to 1
a
20 1,1 to 1,3
30 1,45
40 1,6
50 1,6
a
Force correction factors for material depend on the modulus of elasticity in
the manufacturer's material specification:
2
Typical modulusof elasticity inGN/m
Correctionfactor =
2
100GN/m
7.4.2.4 Multiplier force correction factors for ratio m/(d − a )
1 1
Piston rings made of materials in Classes 30 to 50 increase the tangential force and diametral force in
relationship to the modulus of elasticity (see Table 5) when ratio m/(d − a ) regular is used.
1 1
For limitation of such increased forces, it is common to use reduced values of m/(d − a ). See Table 6 for the
1 1
recommended correction factors m/(d − a ) regular and m/(d − a ) reduced.
1 1 1 1
Table 6 — Force correction factors for ratio m/(d − a )
1 1
Factor
Material class
m/(d − a ) reduced
1 1
m/(d − a ) regular
1 1
Code:MR
10 1 —
20 1 —
30 1 0,825
40 1 0,75
50 1 0,75
For calculation of real values of ratio m/(d − a ) reduced, the factors given in
1 1
Table 6 apply. Therefore, the values of m/(d − a ) calculated with formula given
1 1
in Table 4 shall be corrected with the correction factors given in Table 6.
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ISO 6621-4:2003(E)
7.4.3 Examples for correction of F and F

t d
7.4.3.1 First example — Selected piston ring type: ISO 6622-1 B - 95 ×××× 2,5 - MC53 / MR CR2 IW
7.4.3.1.1 Multiplying factors
These are
 1,6 for material Subclass 53,
 0,75 for ratio m/(d − a ) reduced,
1 1
 0,88 for peripheral surface chromium plated CR2, and
 0,78 for internal step IW.
7.4.3.1.2 Calculation
Total force correction factors: 1,6 × 0,75 × 0,88 × 0,78 = 0,824.
Basic values F and F according to ISO 6622-1: F = 18,5 N and F = 39,8 N.

t d t d
Corrected values: F = 0,824 N × 18,5 N ± 20 % and F = 0,824 N × 39,8 N ± 20 %;
t d
F = 15,2 N ± 20 and F = 32,8 N ± 20 %;
t d
F = 12,2 N . 18,2 N and F = 26,2 N . 39,4 N.
t d
7.4.3.2 Second
...