Designation:F788/F788M–05
Standard Specification for
Surface Discontinuities of Bolts,Screws,and Studs,Inch and Metric Series1
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This standard is issued under thefixed designation F788/F788M;the number immediately following the designation indicates the year of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.
A superscript epsilon(e)indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1.Scope
1.1This specification establishes allowable limits for the various types of surface discontinuities that may occur during the manufacture and processing of bolts,screws,and studs, including heat-treated machine screws,tapping screws,and sems(the washers of screw-washer assemblies are excluded). This specification covers metric series products with nominal diameters of4mm and larger and with specified minimum tensile strengths of800MPa and greater;and inch series products with nominal diameters of No.5(0.1250in.)and larger and with specified minimum tensile strengths of90000 psi and greater.
1.2The values stated in either SI(metric)or inch-pound units are to be regarded separately as standard.The values stated in each system are not exact equivalents,therefore,each system must be used independently of the other.Combining values from the two systems may result in nonconformance with the specification.
1.3When the engineering requirements of the application necessitate control of surface discontinuities on bolts,screws, or studs,the purchaser shall specify conformance to ASTM Specification F788/F788M,in the original inquiry and pur-chase order.
1.3.1When the engineering requirements of the application necessitate that surface discontinuities on bolts,screws,and studs be controlled within limits closer than those specified in this specification,the purchaser shall specify the applicable limits in the original inquiry and purchase order.
1.4The allowable limits established in this specification for metric bolts,screws,and studs with nominal diameters from4 to24mm inclusive,are essentially identical with requirements given in ISO6157/I.There are no ISO standards for surface discontinuities on any inch-series products.
2.Referenced Documents
2.1ASTM Standards:2
E340Test Method for Macroetching Metals and Alloys
F1470Guide for Fastener Sampling for Specified Mechani-cal Properties and Performance Inspection
F1789Terminology for F16Mechanical Fasteners
2.2ISO Standard:3
ISO6157/I Fasteners,Surface Discontinuities on Bolts, Screws and Studs
3.Ordering Information
3.1Orders for bolts,screws,and studs requiring disconti-nuity control shall include the following:
3.1.1ASTM designation and date of issue of this specifica-tion.
3.1.2Special requirements,for example,closer discontinu-ity limits(1.3.1)and inspection sampling plan(6.2).
4.Types of Surface Discontinuities(see Terminology越南国民党
F1789for definitions not provided)
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4.1Crack
4.1.1Quench Cracks—Typical quench cracks are shown in Fig.1.Limits are specified in
5.2.男同姓恋
4.1.2Forging Cracks—Typical forging cracks are shown in Fig.2.Limits are specified in
5.3.
4.2Burst—Typical bursts are shown in Fig.3.Limits are specified in
5.4.
4.2.1Shear Burst—A shear burst is an open break in the metal located at approximately a45°angle to the product axis. Shear bursts occur most frequently at the periphery of products havingflanged or circular heads.Shear bursts may also occur on the sides of hex-head products.Typical shear bursts are shown in Fig.3.Limits are specified in
5.4.
1This specification is under the jurisdiction of ASTM Committee F16on Fasteners and is the direct responsibility of Subcommittee F16.93on Quality Assurance Provisions for Fasteners.
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Current edition approved Oct.1,2005.Published October2005.Originally approved in1982.Last previous edition approved in2002as F788/F788M–02.
2For referenced ASTM standards,visit the ASTM website,,or contact ASTM Customer
Service at For Annual Book of ASTM Standards volume information,refer to the standard’s Document Summary page on the ASTM website.
3Available from American National Standards Institute(ANSI),25W.43rd St., 4th Floor,New York,NY10036.
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4.3Seam —Typical seams are shown in Fig.4.Limits are specified in
5.5.
4.4Fold —Typical folds are shown in Fig.5a ,b ,and c .Limits are specified in
5.
6.
4.5Thread Lap —Limits are specified in Supplementary Requirement S.1.1.
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4.6Void —A void is a shallow pocket or hollow on the surface of a bolt or screw due to nonfilling of metal during forging.V oids are produced by marks or impressions of chips (shear burrs)or by rust formation on the raw material.They are not planished during forging.Typical voids are shown in Fig.6.Limits are specified in
5.7.
4.7Tool Marks —Tool marks are longitudinal or circumfer-ential grooves of shallow depth produced by the movement of manufacturing tools over the surface of the bolt or screw.Typical tool marks are shown in Fig.7.Limits are specified in
5.8.
4.8Gouge —A gouge is an indentation on the surface of a bolt,screw,or stud produced by the forceful abrasion or the impact of a product coming into contact with another product or manufacturing equipment during manufacture,handling,or transport.Limits are specified in
5.9.
5.Allowable Limits
5.1Letter Definitions —Throughout the following require-ments,D designates the nominal size (basic major diameter of thread)of bolts,screws,and studs,except for products with shoulders,in which case D designates the largest shoulder diameter;and Dc designates flange diameter (specified maxi-mum)or head diameter (specified maximum)of circular head products.For metric series products,D and Dc are in millime-tres;for inch-series products,D and Dc are in inches.
5.2Quench Cracks —Quench cracks of any depth,any length,or in any location are not permitted.
5.3Forging Cracks —Forging cracks on the top of the head of bolts and screws are permitted,provided that (a )no crack shall have a length exceeding 1.0D ,and (b )no crack shall have a width or depth exceeding 0.04D .See Note 1.
N OTE 1—Forging cracks within the limits of this specification may be unsightly,but do not affect the mechanical properties or functional requirements of the bolt.
5.4Bursts and Shear Bursts (see Note 2):
5.4.1For hex-head bolts and screws,bursts and shear bursts are permitted,provided that:(1)no burst or shear burst in the flats extends into the crown (chamfer)circle on the top of the head or into the un
derhead bearing circle,(2)no burst or shear burst located at the intersection of two wrenching flats reduces the width across corners below its specified minimum,and (3)no burst or shear burst has a width or depth greater than .06D but not to exceed .062in.(1.6mm).
5.4.2For flange bolts and screws and products with circular heads,bursts and shear bursts at the periphery of the flange or head are permitted,provided that:(1)not more than one burst or shear burst has a width greater than 0.04Dc ,and (2)the width of the one burst or shear burst that exceeds a width of 0.04Dc does not have a width greater than 0.08Dc .
5.4.3For indented head bolts and screws,bursts and shear bursts in the raised periphery of the indented head are permitted,provided that:(1)no burst or shear burst has a width greater than 0.06D ,and (2)no burst or shear burst has a depth extending below the indented portion.
N OTE 2—Bursts and shear bursts within the limits of this specification may be unsightly,but do not affect the mechanical properties or functional requirements of the bolt.
5.5Seams :
5.5.1Seams in the shanks of bolts,screws,and studs are permitted provided that no seam has a depth greater than 0.03D
.
FIG.1Typical Quench
Cracks
FIG.2Typical Forging
Cracks
5.5.2Seams extending into the heads and flanges of bolts and screws are permitted,provided that they do not open beyond the limits specified for bursts and shear bursts in 5.4.5.6Folds :
5.6.1Folds located at interior corners that are at or below the underhead bearing surface,for example,at the junction of head to shank,are not permitted,except for cloverleaf
folds
FIG.3Typical Bursts and Shear
Bursts
FIG.4Typical
Seams
FIG.5Typical
Folds
occurring at the intersection of non-circular shoulders with head bearing face (see Fig.5a ).
5.6.2Folds located at interior corners that are above the underhead bearing surface,for example,at the junction of the hex head with the top of flange of flange bolts and screws,are permitted (see Fig.5b ).
5.6.3Folds located at exterior corners are permitted (see Fig.5c ).5.7Voids :
5.7.1V oids on the surfaces of bolts,screws,and studs are permitted,provided that:(1)depth of voids does not exceed 0.25mm or 0.02D ,whichever is greater,and (2)the combined area of all voids on the underhead bearing surface of bolts and screws does not exceed 10%of the specified minimum bearing surface area.
5.7.2The method for determining the area of voids on the bearing surface shall be as agreed upon between the purchaser and the producer.5.8Tool Marks :
5.8.1Tool marks on the underhead bearing surface are permitted,provided the surface roughness measurement does not exceed 3.2µm or 125µin.,determined as the arithmetic average deviation fro
m the mean surface.
5.8.2Tool marks on other surfaces of the product are permitted.
5.9Nicks and Gouges —Nicks,gouges,dents,and scrapes are permitted,provided that the functionability of the product is not impaired.
6.Inspection and Evaluation
6.1Bolts,screws,and studs shall be inspected for surface discontinuities in accordance with the procedure in 6.2,6.3,and 6.4.
6.2The purchaser shall specify in the original inquiry and purchase order the inspection sampling requirements that the producer must satisfy to demonstrate the acceptability of bolts,screws,and studs with respect to surface discontinuities.
6.3In the absence of purchaser instructions (6.2),inspection and evaluation shall be in accordance with 6.5.
6.4For referee purposes,unless other procedures have been specified by the purchaser (6.2),inspect
ion and evaluation shall be in accordance with 6.5.6.5Inspection Procedure :6.5.1Visual Inspection :
6.5.1.1A random sample shall be taken from the lot in accordance with F 1470and examined visually (magnetic particle or fluid penetrant are recommended)for the presence of quench cracks,forging cracks,bursts,shear bursts,seams,folds,voids,tool marks,and nicks and gouges.Visual inspec-tion can include the use of devices that provide up to,and including,10-power magnification.
6.5.1.2If,during this inspection,any products are found with quench cracks in any location or with folds at interior corners that are at or below the underhead bearing surface,the lot may be rejected by the purchaser.
6.5.1.3If,during this inspection,any products are found with any other surface discontinuity,each discontinuity shall be measured,and if any is found that exceeds the allowable dimensional limits for that discontinuity as specified in Sec-tion 5,the lot may be rejected by the purchaser.
7.Keywords
7.1bolts;crack;discontinuities (surface);fold;screw (ma-chine,sems,tapping);seam;studs;thread lap;
void
FIG.6Typical
Voids
FIG.7Typical Tool
Marks
SUPPLEMENTARY REQUIREMENTS
One or more of the following supplementary requirements shall apply only when specified by the purchaser in the inquiry and order.Supplementary Requirements shall in no way negate any requirement of the specification itself.
S1.Assemblies Subject to Severe Dynamic Stresses
S1.1Laps in Screw Threads:
S1.1.1Laps of any depth and any length which originate below(or originating above and extending b
elow)a point located at a distance equal to or less than20%of the thread height,measured from the minor diameter,are not permitted. See4.5and the Fig.S1.1and Fig.S1.2.
S1.1.2Surface discontinuities of threads caused by the thread rolling process,as in Fig.S1.2,shall be excluded from these requirements provided the discontinuities do not exceed the depth of0.5%3nominal diameter and are essentially parallel to the adjacent thread contour and are not directed toward the screw or bolt axis.
S1.2Thread Lap Inspection:
S1.2.1Visual Inspection—A random sample shall be se-lected from the lot in accordance with F1470.The sample selected shall be surface etched in a50%solution of HCl and H2O at approximately180°F(no more than5min of etch time should be employed as excessive etching may remove shallow thread laps).After etch,the samples shall be examined under a 103magnification for the presence of laps.
S1.2.2Microscopic Examination—If laps are present,one of the samples shall be sectioned longitudinally on the center line of the bolt/screw and on a plane passing through the point at which any lap extends closest to the minor diameter of the thread.The section shall be etched for microsco
pic examina-tion in accordance with Test Method E340.Acceptance shall be based on the requirements of
S1.1. FIG.S1.1Typical Thread
Laps
