Table 3. External Inch Screw Thread Calculations for 1 ∕
2 -28 UNEF-2A
Characteristic Description
Calculation
Notes
. 2 1 05 05000 .
d bsc = = =
d bsc is rounded to four decimal places
Basic major diameter, d bsc
. . P 28 = 1 = 0 035714285714 0 03571429 =
P is rounded to eight decimal places
Pitch, P
Maximum external major diameter ( d max ) = basic major diameter ( d bsc ) − allowance ( es )
d d es max bsc = −
es is the basic allowance
. d 05000 bsc =
Basic major diameter ( d bsc )
d bsc is rounded to four decimal places
. es =
0300
Td 2 for Class 2 # A
Allowance ( es )
Td 2 is the pitch diameter tolerance for Class 2A
3 1
3 2
. 0 0015 0 0015 . D +
. 0015
Td
LE
P
=
+
2
External pitch diameter tolerance Td 2
LE = 9 P (length of engagement) Td 2 is rounded to six decimal places
3 1
3 2
. . . 0 0015 0 5 0 0015 9 0 03571429 0 015 0 03571429 0 001191 0 000850 0 001627 0 003668 . . . . . . . # # + + + + = ^
h
= =
. . es 0 300 0 003668 0 0011004 0 0011 # = = = . . . . d d es 0 5000 0 0011 0 4989 max base = − = − = .
Allowance ( es )
es is rounded to four decimal places d max is rounded to four decimal places
Maximum external major diameter ( d max ) Minimum external major diameter ( d min ) = maximum external major diameter ( d max ) − major diameter tolerance ( Td )
d d Td min max = −
Td is the major diameter tolerance
. . . P 0060 0 060 0 03571429 0 060 0 001276 0 060 0 108463 0 00650778 0 0065 3 2 2 3 3 # # # = = = = = = . . . . . .
Td
Td is rounded to four decimal places
Major diameter tolerance ( Td )
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