Unified National Fine | Drill diameters for tapping threads | ||
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UNC No.2 - UNF No.12 | Thread pitch (P) | ![]() cutting tap |
![]() roll tap |
ø | TPI | ø mm | ø mm |
No.2 | 64 | 1.90 | 2.00 |
No.3 | 56 | 2.15 | 2.30 |
No.4 | 48 | 2.40 | 2.60 |
No.5 | 44 | 2.70 | 2.90 |
No.6 | 40 | 2.95 | 3.20 |
No.8 | 36 | 3.50 | 3.90 |
No.10 | 32 | 4.10 | 4.50 |
No.12 | 28 | 4.70 | 5.10 |
Unified National Fine | Drill diameters for tapping threads | ||
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UNF 1/4 - UNF 1.1/2 | Thread pitch (P) | ![]() cutting tap |
![]() roll tap |
ø | TPI | ø mm | ø mm |
1/4 | 28 | 5.50 | 6.00 |
5/16 | 24 | 6.90 | 7.50 |
3/8 | 24 | 8.50 | 9.10 |
7/16 | 20 | 9.90 | 10.60 |
1/2 | 20 | 11.50 | 12.10 |
9/16 | 18 | 12.90 | |
5/8 | 18 | 14.50 | 15.30 |
3/4 | 16 | 17.50 | 18.30 |
7/8 | 14 | 20.40 | |
1 | 12 | 23.25 | |
1.1/8 | 12 | 26.50 | |
1.1/4 | 12 | 29.50 | |
1.3/8 | 12 | 32.75 | |
1.1/2 | 12 | 36.00 |
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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