для заказа - kyocera@kyocera-tools.ru TAP CLASSES AND SIZE
TAPS ENGINEERING DATA
CLASS OF FIT / CLASSES OF THREADS / TAP SIZE (cont.)
On Charts 2A and 2B (below), examples of the relationship of machining situations, as can the H1 limit (+.0005” over basic DRILLS
Class of Fit to various tap limit sizes is shown for both Imperial P.D.). However, tool wear would force the discarding of the H1 tap
and Metric sizes. In chart 2A, using a 1/4”-20NC or UNC thread long before the H5 would be worn to an undersize condition. The
size, it is obvious that an H5 limit (+.0025” over basic pitch rule is obvious: always select the largest “H” limit possible
diameter) can be used to cut the tightest class of thread in most to achieve proper class of fit, and maximum tool life.
CHART 2A COMPARISON OF PITCH DIAMETER LIMITS TO CLASS OF FIT END MILLS
0.2255 CLASS OF THREAD TAP LIMIT 0.2255
0.2245 0.2245
0.2235 1B0.2248 0.2235 ROUTERS
0.2225
BASIC 0.2225 Tol. 0.2224 0.2211 3B0.2211 0.2201 H5 0.2215 THREAD MILLS
PITCH 0.2215 0.0073 H4 Tol .0005 0.2205 & TAPS
0.2205 2B 2 Tol. 3 H3 Tol .0005 0.2195
DIA. 0.2195 0.0036 H2 Tol .0005 0.2185
0.2185 Tol. Tol. Tol. H1 Tol .0005 0.2175
0.2175 0.0049 0.0036 0.0026 Tol .0005 0.2165
0.2165 Tol .0005
L1
Chart 2B shows the same relationship with a metric thread. Using However, tool wear would force the discarding of the D1 tap long ENGRAVERS
a M6 X 1.0, it is obvious that a D5 limit (+.0025” over basic pitch before the D5 would be worn to an undersize condition. The rule
diameter) can be used to cut the standard class of thread in most is obvious: always select the largest “D” limit possible to BORING BARS
machining situations, as can the D1 limit (+.0005” over basic P.D.). achieve proper class of fit, and maximum tool life.
CHART 2B COMPARISON OF PITCH DIAMETER LIMITS TO CLASS OF FIT
0.2186 CLASS OF THREAD TAP LIMIT 0.2186
0.2176 0.2181 0.2176 REAMERS
0.2166 0.2166
7H
0.2156 0.2165 0.2156
0.2146 0.2146
0.2136 6H 0.2152 D7 0.2136
0.2126 D5 0.2126
0.2116 5H 0.2144 SAWS
0.2106 0.2116
4H D4 0.2106
0.2096 D3
BASIC Tol. Tol. Tol. Tol. D1 D2 0.2096
PITCH 0.0075 0.0059 0.0046 0.0037
DIA. DU1
P.D. TOL. = .0010 TECHNICAL
SCREW THREAD CLASSES OVERVIEW
Screw thread classes are distinguished from each other by the which minimizes galling and seizure encountered in assembly
amount of tolerance and allowance. Class 1A and Class 1B: and use. It also accommodates, to a limited extent, plating,
The combination of Class 1A for external threads and Class finishes or coatings. Class 3A and 3B: The combination INDEX
1B for internal threads is intended to cover the manufacture of of Class 3A for external threads and Class 3B for internal
threaded parts where quick and easy assembly is necessary threads is provided for those applications where closeness
or desired, and an allowance is provided to permit ready of fit and accuracy of lead and angle of thread are important.
assembly. Class 2A and Class 2B: The combination of Class These threads are obtained consistently only by use of high
2A for external threads and Class 2B for internal threads quality production equipment supported by a very efficient
designed for screws, bolts and nuts, is also suitable for a system of gauging and inspection. No allowance is provided.
variety of other applications. A similar allowance is provided
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