19
PM-1236 v4 1-2017.indd
Figure 3-21 Using the threading dial
The dial worm gear has 16T; the leadscrew is 8 TPI,
so the carriage moves 2 inches for each revolution of
the dial when the split-nut is disengaged (when the
split-nut is engaged the dial is stationary).
The symbol "/" in the table means "forget the dial"
— engage at random for any TPI value that is an
even multiple of 4. For all other standard TPI threads
the split-nut is engaged when the datum coincides
with a specific line — or lines — on the threading dial.
1 - 8 Not the same as "/" (re-engage anywhere). Ap-
plies to TPI values that are odd multiples of 4; start on
any line (not a half space), re-engage on any line.
2.4.6.8 Applies to even number TPI values that are not multiples of 4 (10, 14, etc.): re-engage at the line you started with OR
any other line at right angles to it — start on 1, re-engage on 3, 5 or 7; or, start on 2, re-engage on 4, 6 or 8.
4.8 Applies to odd number TPI values (7, etc.): re-engage at the line you started with OR the diametrically opposite line — can
be any line pair, 1 & 5, 2 & 6, etc., not necessarily 4 & 8.
8 Applies to fractional values (4-1/2, etc.): re-engage on the same line you started with for the first pass — can be any line
number, not just the 8.
TPI Line TPI Line TPI Line TPI Line
4 / 8 / 16 / 32 /
4-1/2 8 9 4.8 18 2.4.6.8 36 1 - 8
9-1/2 8 19 8 38 2.4.6.8
5 4.8 10 2.4.6.8 20 1 - 8 40 /
5-1/2 8 11 4.8 22 2.4.6.8 44 1 - 8
6 4.8 12 1 - 8 24 / 48 /
6-1/2 8 13 4.8 26 2.4.6.8 52 1 - 8
7 4.8 14 2.4.6.8 28 1 - 8 56 /
7-1/2 8 15 4.8 30 2.4.6.8
THREADS PER INCH
UPPER
GEAR 24T
Speed
MII
16 18 19 20 22 24 26 28 30
MI
32 36 38 40 44 48 52 56 60
Gearbox A2 A3 C3 A4 C3 C3 C3 A5 B4
Lower gear 48T, exceptions in RED 38 44 52
THREADS PER INCH
UPPER
GEAR 48T
Speed
MII
4 4-1/2 9-1/2 5 5-1/2 6 6-1/2 7 7-1/2
MI
8 9 19 10 11 12 13 14 15
Gearbox A2 A3 C3 A4 C3 C3 C3 A5 B4
Lower gear 24T, exceptions in RED 38 22 26
Figure 3-20 Gear-
box and external
gear selections
for standard
threads
Figure 3-22
Threading dial
visualization for
selected U.S.
threads
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