Table 2c. Limiting Dimensions of ANSI General Purpose Acme Single-Start Screw Threads ANSI/ASME B1.5-1997 (R2014) Nominal Diameter, D 1 1 ∕ 2 1 3 ∕ 4 2 2 1 ∕ 4 2 1 ∕ 2 2 3 ∕ 4 3 3 1 ∕ 2 4 4 1 ∕ 2 5 Threads per Inch a 4 4 4 3 3 3 2 2 2 2 2 Limiting Diameters External Threads Classes 2G, 3G, and 4G { Max ( D ) 1.5000 1.7500 2.0000 2.2500 2.5000 2.7500 3.0000 3.5000 4.0000 4.5000 5.0000 Major Diameter Min 1.4875 1.7375 1.9875 2.2333 2.4833 2.7333 2.9750 3.4750 3.9750 4.4750 4.9750 Classes 2G, 3G, and 4G Minor Diameter Max 1.2300 1.4800 1.7300 1.8967 2.1467 2.3967 2.4800 2.9800 3.4800 3.9800 4.4800 Class 2G, Minor Diameter Min 1.1965 1.4456 1.6948 1.8572 2.1065 2.3558 2.4326 2.9314 3.4302 3.9291 4.4281 Class 3G, Minor Diameter Min 1.2144 1.4640 1.7136 1.8783 2.1279 2.3776 2.4579 2.9574 3.4568 3.9563 4.4558 Class 4G, Minor Diameter Min 1.2189 1.4686 1.7183 1.8835 2.1333 2.3831 2.4642 2.9638 3.4634 3.9631 4.4627 Class 2G, Pitch Diameter { Max 1.3652 1.6145 1.8637 2.0713 2.3207 2.5700 2.7360 3.2350 3.7340 4.2330 4.7319 Min 1.3429 1.5916 1.8402 2.0450 2.2939 2.5427 2.7044 3.2026 3.7008 4.1991 4.6973 Class 3G, Pitch Diameter { Max 1.3677 1.6171 1.8665 2.0743 2.3238 2.5734 2.7395 3.2388 3.7380 4.2373 4.7364 Min 1.3573 1.6064 1.8555 2.0620 2.3113 2.5607 2.7248 3.2237 3.7225 4.2215 4.7202 Class 4G, Pitch Diameter { Max 1.3701 1.6198 1.8693 2.0773 2.3270 2.5767 2.7430 3.2425 3.7420 4.2415 4.7409 Min 1.3627 1.6122 1.8615 2.0685 2.3181 2.5676 2.7325 3.2317 3.7309 4.2302 4.7294 Internal Threads Classes 2G, 3G, and 4G { Min 1.5200 1.7700 2.0200 2.2700 2.5200 2.7700 3.0200 3.5200 4.0200 4.5200 5.0200 Major Diameter Max 1.5400 1.7900 2.0400 2.2900 2.5400 2.7900 3.0400 3.5400 4.0400 4.5400 5.0400 Classes 2G, 3G, and 4G { Min 1.2500 1.5000 1.7500 1.9167 2.1667 2.4167 2.5000 3.0000 3.5000 4.0000 4.5000 Minor Diameter Max 1.2625 1.5125 1.7625 1.9334 2.1834 2.4334 2.5250 3.0250 3.5250 4.0250 4.5250
Min Max Min Max Min Max
1.3750 1.3973 1.3750 1.3854 1.3750 1.3824
1.6250 1.6479 1.6250 1.6357 1.6250 1.6326
1.8750 1.8985 1.8750 1.8860 1.8750 1.8828
2.0833 2.1096 2.0833 2.0956 2.0833 2.0921
2.3333 2.3601 2.3333 2.3458 2.3333 2.3422
2.5833 2.6106 2.5833 2.5960 2.5833 2.5924
2.7500 2.7816 2.7500 2.7647 2.7500 2.7605
3.2500 3.2824 3.2500 3.2651 3.2500 3.2608
3.7500 3.7832 3.7500 3.7655 3.7500 3.7611
4.2500 4.2839 4.2500 4.2658 4.2500 4.2613
4.7500 4.7846 4.7500 4.7662 4.7500 4.7615
{
Class 2G, Pitch Diameter
{
Class 3G, Pitch Diameter
{
Class 4G, Pitch Diameter
a All dimensions are given in inches. The selection of threads per inch is arbitrary and for the purpose of establishing a standard.
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