British Standard Whitworth | Drill diameters for tapping threads | ||
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BSW 3/32 - BSW 1/4 | Thread pitch (P) | ![]() cutting tap |
![]() roll tap |
ø | TPI | ø mm | ø mm |
3/32 | 48 | 1.85 | 2.10 |
1/8 | 40 | 2.55 | 2.90 |
5/32 | 32 | 3.20 | 3.60 |
3/16 | 24 | 3.70 | 4.30 |
7/32 | 24 | 4.50 | |
1/4 | 20 | 5.10 | 5.80 |
British Standard Whitworth | Drill diameters for tapping threads | ||
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BSW 5/16 - BSW 2 | Thread pitch (P) | ![]() cutting tap |
![]() roll tap |
ø | TPI | ø mm | ø mm |
5/16 | 18 | 6.50 | 7.30 |
3/8 | 16 | 7.90 | 8.80 |
7/16 | 14 | 9.20 | 10.20 |
1/2 | 12 | 10.50 | 11.60 |
9/16 | 12 | 12.00 | 13.20 |
5/8 | 11 | 13.50 | 14.70 |
3/4 | 10 | 16.50 | 17.70 |
7/8 | 9 | 19.25 | 20.75 |
1 | 8 | 22.00 | 23.75 |
1.1/8 | 7 | 24.75 | |
1.1/4 | 7 | 28.00 | |
1.3/8 | 6 | 30.50 | |
1.1/2 | 6 | 33.50 | |
1.5/8 | 5 | 35.50 | |
1.3/4 | 5 | 39.00 | |
1.7/8 | 4.1/2 | 41.50 | |
2 | 4.1/2 | 41.50 |
Roll tap
A roll tap or forming tap usually has a longer life and works faster. It produces no chips, a stronger thread and is also suitable for blind holes. A disadvantage is the higher purchase price. In addition, much more machine power is required to let the forming tap do its job (approx. 50% higher compared to cutting tapping). Special attention is needed for the right lubricant because of friction and with a lot of heat development as a result.
Cutting tap
With a cutting tap - usually called a thread tap - the thread is cut by machining. A tap is usually made of HSS (High Speed Steel) and has sharply ground cutting teeth. A lubricant is also used for tapping. The supply of cutting oil and the removal of the chips takes place through the recessed grooves of the tap. A set of taps usually consists of: 3 taps for metric threads, 2 taps for gas threads, 1 tap for machine taps. There are taps for the generally used right-hand thread, but also for left-hand thread.
Lubricants
When tapping, a lubricant suitable for the material is used, which serves to lubricate and cool. Today there are excellent universal oils available, for example drilling oil, cutting oil, tap oil, even 3 in 1 in aerosol.
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