Machinery's Handbook, 31st Edition
BUTTRESS THREADS 2085 confirmed by a simplified view showing thread angles on the drawing of the product that has the buttress thread. Standard Buttress Threads: A buttress thread is considered to be standard when: 1) op- posite flank angles are 7-degrees and 45-degrees; 2) basic thread height is 0.6 p ; 3) toler- ances and allowances are as shown in Table 4 and Table 5 ; and 4) length of engagement is 10 p or less. Thread Designation Abbreviations: In thread designations on drawings, tools, gages, and in specifications, the following abbreviations and letters are to be used: BUTT for buttress thread, pull type
PUSH- BUTT
for buttress thread, push type
Note: Absence of LH indicates that the thread is a right-hand thread.
LH
for left-hand thread
P L A B
for pitch for lead
Note: Absence of A or B after thread class indicates that designation covers both the external and internal threads.
for external thread for internal thread for special for flat root thread for pitch diameter for threads per inch
Le SPL FL
for length of thread engagement
E
TPI THD
for thread Designation Sequence for Buttress Inch Screw Threads: When designating single-start standard buttress threads the nominal size is given first, the threads per inch next, then PUSH if the internal member is to push, but nothing if it is to pull, then the class of thread (2 or 3), then whether external (A) or internal (B), then LH if left-hand, but nothing if right-hand, and finally FL if a flat root thread, but nothing if a radiused root thread; thus, 2.5-8 BUTT-2A indicates a 2.5 inch, 8 threads per inch buttress thread, Class 2 external, right-hand, internal member to pull, with radiused root of thread. The designation 2.5-8 PUSH-BUTT-2A-LH-FL signifies a 2.5 inch size, 8 threads per inch buttress thread with internal member to push, Class 2 external, left-hand, and flat root. A multiple-start standard buttress thread is similarly designated but the pitch is given instead of the threads per inch, followed by the lead and the number of starts is indicated in parentheses after the class of thread. Thus, 10-0.25P-0.5L - BUTT-3B (2 start) indicates a 10-inch thread with 4 threads per inch, 0.5 inch lead, buttress form with internal member to pull, Class 3 internal, 2 starts, with radiused root of thread.
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