Общий каталог Widia 2017

Ground Thread Tap Limits

In addition to the nominal size and pitch of a tap, there is another	Figure 1 Illustrates the numbering system and the .0005" diameter
important dimensional factor to be considered when selecting a	increment separation between successive limits. Because
ground thread tap for a given job. This factor is the pitch diameter	the starting point is basic pitch diameter, dividing the limit
tap limit, “H” and “L”. “H” represents (high) above basic pitch	number by two establishes, in thousandths of an inch, the
diameter; “L” (low) is below basic pitch diameter. Tap limits have	amount the maximum tap pitch diameter is above basic
been established to provide a choice in the selection of the tap size	in the “H” series and the amount the minimum tap pitch
best suited to produce the class of thread desired.	diameter is under basic in the “L” series.

Figure 2 Illustrates the positioning of the tap limits in relation to the various classes of threads for a 1/4–20 size.

Figure 1

.0050 .0050 H10

.0045 This chart shows the .0045

method of designating limits H9 and does not indicate .0040 .0040

available taps in any H8 particular size. .0035 .0035 H7 .0030 .0030 H6

H3 .0010 .0010 H2 .0005 .0005

H1 basic basic

P.D. For sizes from 1–1-1/2" P.D.

L1 inclusive, 6 TPI and fi ner .0005 For taps through 1" inclusive, 8 TPI and fi ner

Figure 2 Class of Thread – 1/4–20 UNC and NC .2255 .2255

.2245 .2248 .2245

tap limits tapping hole limits .2235 .2235

.2225 .2225 .2248 .2215 .2215 1B .2211 .2211 .2205 .2205 H5 2B TOL.0005 .2201

H1	TOL.0005	TOL	TOL	TOL	TOL	TOL
		.0073	.0049	.0036	.0036	.0026

basic TOL.0005 .2175 .2175 P.D. TOL.0005 L1

.2165 .2165