ASME B188.8.131.52 pdf download Metric Formed Hex Screws
6.6 Thread Length The length of thread on screws shall be controlled by the maximum grip length, L g , and the minimum body length, L s , as set forth in this section.
6.6.1 Grip Gaging Length, L g . The grip gaging length, L g , is the distance, measured parallel to the axis of the screw, from the underhead bearing surface to the face of a noncounterbored or noncountersunk standard GO thread ring gage assembled by hand as far as the thread will permit. For standard diameter-length com- binations of screws that are not threaded full length, the values for L g max. are specified in Table 5. For diameter- length combinations not listed in Table 5, the maximum grip gaging length, as calculated and rounded to one decimal place, shall be equal to the nominal screw length, L, minus the reference nominal thread length, B,as specified in Table 8 ( L g max. = L – B ). L g max. shall be used as a criterion for inspection. For screws of nominal lengths, L , that are equal to or shorter than the lengths specified in Table 8 for screws threaded full length, L g max. = L u max. as specified in Table 8.
6.6.2 Body Length，Ls. Body length，Lsp is the dis-tance, measured parallel to the axis of the screw, fromthe underhead bearing surface to the last scratch ofthread or top of the extrusion angle, whichever is clos-est to the head. For standard diameter-length combina-tions of screws that are not threaded full length,thevalues of Le min. are specified in Table 5.For diameter-length combinations not listed in Table 5, the minimumbody length, as calculated and rounded to one decimalplace, shall be equal to the maximum grip gaging lengthascomputed, minus the transition thread lengthasspec-ified inTable8(Lgmin.=Lg max.- X ref.).Lgmin.shallbe used as a criterion for inspection. For screws that arethreaded full length, the distance from the underheadbearing surface to the face of a noncounterbored or non-counter-sunk standard GO thread ring gage assembledby hand as far as the thread will permit shall not exceedthe length,Le， as specified in Table 8.For screwsthreaded full length, the last scratch of thread must notbe within the maximum filletlength, F1max., asspeci-fied in Table 3: L min.=F max.
6.6.3 Thread Length，B. Thread length，B,a refer-ence dimension, as specified in Table 8, is intended forcalculation purposes only , and is the distance, measuredparallel to the axis of the screw, from the extreme endof the screw to the last complete (full form) thread.
6.6.4 Transition Thread Length,X. The transitionthread length,X,as specified in Table 8, is a referencedimension intended for calculation purposes only. It in-cludes the length of incomplete threads and tolerances on grip gaging length and body length. The transition from full thread to incomplete thread shall be smooth and uniform. The major diameter of the incomplete threads shall not exceed the actual major diameter of the complete (full form) threads. The transition threads shall have a rounded root contour.
6.6.5 Position of Body-to-Thread. For products with cut threads, at maximum material condition, the axis of the screw body, D s (derived median line), over a length equal to the nominal screw diameter from the last scratch of thread, shall be within the positional tol- erance zone diameter specified in Table 2 with respect to the axis of the thread, over a length equal to the nom- inal screw diameter from the last complete thread. A gage and gaging procedure for checking body position is given in Nonmandatory Appendix B.
6.7 Screw Threads
6.7.1 Thread Series and Tolerance Class. Screw threads shall be general purpose metric screw threads with tolerance Class 6g conforming to ASME B1.13M, unless otherwise specified by the purchaser. For screws with additive finish, size limits for tolerance Class 6g apply prior to coating, and the thread after coating is subject to acceptance using a basic (toler- ance position h) size GO thread gage and tolerance Class 6g thread gage for either minimum material LO or NOT GO.
6.7.2 Thread Gaging. Unless otherwise specified, dimensional acceptability of screw threads shall be based on System 21 of ASME B1.3M. 6.8 Materials and Mechanical Properties 6.8.1 Steel. Unless otherwise specified, steel screws shall conform to the requirements of ASTM F 568M.
6.8.2 Corrosion-Resistant Steels. Unless other- wise specified, screws made of corrosion-resistant steels shall conform to the requirements of ASTM F 738M. 6.8.3 Nonferrous Metals. Unless otherwise speci- fied, nonferrous screws shall conform to the require- ments of ASTM F 468M.
6.9 Finish Unless otherwise specified, screws shall be supplied with a natural (as processed) finish, unplated or un- coated, in a clean condition and lightly oiled.