For measuring pitch diameter of threads, and tap.

Model No.	Wire Dia. (mm)	Metric (pitch)	Whitworth (TPI)	US Std. (TPI)
TW-0.170	0.170	0.25/0.30		80
TW-0.195	0.195			72
TW-0.220	0.220	0.35		64
TW-0.250	0.250	0.40	60	56
TW-0.290	0.290	0.45/0.5		56
TW-0.335	0.335	0.60	48/40	48/44
TW-0.390	0.390
TW-0.455	0.455	0.70/0.75/0.80		36/32
TW-0.530	0.530	0.90	32/28	28
TW-0.620	0.620	1.0	26/24	24
TW-0.725	0.725	1.25	22/20/19	20
TW-0.895	0.895	1.50	18/16	18/16
TW-1.100	1.100	1.75	14	14
TW-1.350	1.350	2.0	12/11	12/11
TW-1.650	1.650	2.50	10/9	10/9
TW-2.050	2.050	3.50	8	8/7
TW-2.550	2.550	4.0	6	6
TW-3.200	3.200	5.0/5.50/6.0	5/4½	5/4½

TW-9018S: Range: 0.170-3.200mm 18 pair / set    Clamp Hole Φ6.5mm or Φ6.35mm

Remark: Efficient dia. (pitch dia.)    Formula: E= M+0.866025p-3dm    Dia. (MPE): 0.001mm