ASME B18.6.3:1998 pdf download MACHINE SCREWS AND MACHINE SCREW NUTS
2.3 Threads
2.3.1 Machine Screws. The threads on machinescrews, except for the No.0000.No.000,and No. 00 sizes. which are cuvered in Appendix V,shall beUnified Standard,Class 2A,UNC and UNF series, orUNRC and UNRF serics, at option of manufacturer,in accurdance wit ASME Bi.i. For threads withadditive finish, the maximum diametcrs of Class 2Amay be cxceeded by the amount of thc allowancc; thatis, the Class 2A maximum diamcters shall apply to anunplaled or uncoated part, or to a part before platingor coating, whercas the basic diameters (Class 3A GO)shall apply to a part after plating or coating. Theminimum major diameter of plated or coated screwsmay approach but shall not be less than the Class 2Aminimum !imit
2.3.2 Machine Screw Nuts. Threads shall beUnified Standard, Ciass 2B，UNC or UNF series forhexagon muchine screw nuts, and UNC series for squarcmnachine screw nuts,in accordancc with ASME B1.1
2.4 Length of Thread
2.4.1 Machine Screws. Machine screws shall havethread leneths conforming to the following (on screwsthreaded full length, the distance to first full formthread shall be measured, parallel to the axis of screw,from the bearing surface of the head to the face of anonchamnfered or noncounterbored slandard 3A GOthread ring gage assembled by hand as far as the threadwill permit)
fa) Sizes No.5 and Smailer.Sewsnomtnalengths equal to three diameters and shorter shall havcfull form threads extending to within one pitch (thrcad)of the bearing surfacc of the hcad, or closcr, if practicablc.Nominal lengths grcater than three diameters,upto and including 1/ in, shall have full form threadsextending to within two pitches (threads) of the bearingsurface of the head, or eloser, if practicable, Screws oflonger nominal lengths shall, unless otherwise specifiedhave a minimum length of full form thread of I in.
(b) Sizes No. 6 and Larger. Screws of nominallengths equal to thrce diameters and shorter shall havefull form threads extending to within one pitch (thread)of the bearing surface of the head, or closer, if practicable. Nominal lengths greater than three diameters. upto and including 2 in., shall have full form threadsextending to within fwo nitches (threads) of the bearingsurface of the head, or closer, if practicable. Screws oflonger nominal lengths shall. unless otherwise specifiedhave a minimum iength of fuli form thread of i.50 in.
2.5 Points
Unless otherwise specified, machine screws shallhave piain sheared ends. Where so specified. headerpoints slrail be as shown in Table 17. Other points orpointing of lunger lengths to header point dimensionsmay rcquire tmachining.
2.6 Diameter of Body
2.6,1 Machine Screws. Thc diameter of budy unmachinc scrcws having other than trim heads shali nutbe less than the Class 2A thrcad minimum pitch diameternor greater than the basic major diameter of thc thread.
2.6.2 Trim Head Machine Screws.The diameterof body on trim head machine screws shall not be lessthan the Ciass 2A thread minimum pitch diameter norgreater than the basic major diameter of the thread.Scrcws not threaded to the hcad shall have a 0.062in. minimum iength shoulder under the fcad withdiameter limits as specified in the dimensional tables
2.7 Material
2.7.1 Machine Screws. Unless otherwise speci-fied, machine screws shall be fabricated from carbonsteci and shaii have a minimum tensile strength of60,000 psi.
Machinc screws, where so specified,ay also bemade from higher strength steeis, corrosion resistantstccl, brass,moncl, aluminum alloys, or other matcrials.as agrced upon between the manufacturer and thepurchaser.
ASME B18.6.3:1998 pdf download
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