Tandem or dual style Acme taps produce Acme threads in a single pass using two sections: a 45° included angle roughing section for easier cutting and greater stock removal, followed by a 29° finishing section that corrects the angles and finishes the thread to proper size. The last few threads of the roughing section guide the finishing section. These taps are designed for through hole applications only and should never be reversed from the hole.
What are tandem Acme taps?
Tandem Acme taps are manufactured in 2 sections. The first threaded section has a 45° included angle, which permits easier roughing thread formation giving freer cutting action and greater stock removal. The last few threads of the roughing section are a guide for the 29° finishing section, which corrects the angles and finishes the thread formation to proper size.
Can tandem Acme taps be reversed in the hole?
No, tandem Acme taps are designed for through hole applications only and should never be reversed from the hole.
Tandem Acme tap dimension table
Complete dimensions for tandem Acme taps from 1/4-16 through 2-4 pitch, including overall length, thread end length, round shank dimensions, square shank dimensions, and maximum depth of nut for different materials.
| SIZE AND PITCH | A OVERALL LENGTH | B LENGTH THREAD END | C LENGTH | D DIA. | E LENGTH | F ACROSS FLATS | MAXIMUM DEPTH OF NUT BRONZE & STEEL | MAXIMUM DEPTH OF NUT BRASS & CAST IRON |
|---|---|---|---|---|---|---|---|---|
| 1/4-16 | 3″ | 1 3/4 | 1″ | .185 | 1/4 | .138 | 1/2 | 3/4 |
| 5/16-14 | 3 13/32 | 1 7/8 | 1 1/4 | .220 | 9/32 | .165 | 5/8 | 7/8 |
| 3/8-12 | 4 1/16 | 2 1/8 | 1 5/8 | .255 | 5/16 | .191 | 5/8 | 1″ |
| 1/2-10 | 5″ | 2 9/16 | 2″ | .367 | 7/16 | .275 | 1″ | 1 1/2 |
| 5/8-8 | 6 1/4 | 3 3/16 | 2 1/2 | .480 | 9/16 | .360 | 1 1/4 | 1 7/8 |
| 3/4-6 | 7 15/16 | 4 5/16 | 3″ | .542 | 5/8 | .406 | 1 1/2 | 2 1/4 |
| 7/8-6 | 8 5/8 | 4 3/8 | 3 1/2 | .697 | 3/4 | .523 | 1 3/4 | 2 5/8 |
| 1″-5 | 10 1/8 | 5 1/4 | 4″ | .697 | 3/4 | .523 | 2″ | 3″ |
| 1 1/8-5 | 10 3/4 | 5 1/4 | 4 1/2 | .800 | 13/16 | .600 | 2 1/4 | 3 3/8 |
| 1 1/4-5 | 11 1/8 | 5 1/4 | 4 3/4 | .896 | 7/8 | .672 | 2 1/2 | 3 3/4 |
| 1 3/8-4 | 12 1/4 | 5 7/8 | 5 1/8 | 1.108 | 1 1/4 | .831 | 2 3/4 | 4 1/8 |
| 1 1/2-4 | 12 5/8 | 5 7/8 | 5 1/2 | 1.233 | 1 1/4 | .925 | 3″ | 4 1/2 |
| 1 3/4-4 | 13 3/8 | 5 7/8 | 6 1/4 | 1.430 | 1 1/4 | 1.072 | 3 1/2 | 5″ |
| 2″-4 | 14 7/8 | 6 1/2 | 7 | 1.644 | 1 3/8 | 1.233 | 4″ | 6″ |
Dimension definitions
- A (Overall Length): Total length of the tandem Acme tap.
- B (Length Thread End): Length of the threaded portion at the end of the tap.
- C (Length): Length of the round shank section.
- D (Dia.): Diameter of the round shank.
- E (Length): Length of the square shank section.
- F (Across Flats): Dimension across the flats of the square shank.
- Maximum Depth of Nut: Recommended maximum nut depth for bronze and steel versus brass and cast iron materials.
Source and updates
Source: taylortool.com engineering data. Reviewed September 2026.