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T-Slot Bolt Dimensions (DIN 787, M6 to M24)

Guide · Updated October 28, 2026

DIN 787 covers bolts for T-slots. The head width a, head length e, head height k and length-thread pairs below agree across the Elesa+Ganter DIN 787 sheet, the J.W. Winco DIN 787 sheet and the fasteners.eu DIN 787 table. Skipped: the M6 x 63 length (one source only), 16, 20 and 24 mm slots (one catalog only), and the 5, 36, 42, 48 and 54 mm sizes (no dimensions in our sources). Head width a is toleranced -0.3/-0.5; e and k are -0.5 (-1 on the 28 mm size). Check the current edition or your supplier for critical work.

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Step by step

Measure the slot: Measure the T-slot neck width with calipers; the DIN 787 size number is that slot width (14, 18, 22 mm and so on).
Pick the bolt row: Find the slot in the chart; it gives the thread (M12 for a 14 mm slot, M16 for 18 mm, M20 for 22 mm).
Check the head fits: Head width a is 0.3 to 0.5 mm under the slot, and head height k must clear the slot undercut depth.
Choose length l: Stack clamp, washer and nut, add spare thread, and pick the next standard length l.
Check thread length b: Make sure the nut lands on threaded length b, not the plain shank.
Slide in and torque: Slide the head in from the slot end, set the clamp, then tighten the nut to the bolt grade.

DIN 787 T-slot bolt dimensions (mm)

Columns: slot width (= head width a nominal), thread d, head length e, head height k, standard length l - thread length b.

Slot a | Thread d | Head e | Head k | l - b
6 | M6 | 10 | 4 | 25-15, 40-28
8 | M8 | 13 | 6 | 32-22, 50-35
10 | M10 | 15 | 6 | 40-30, 63-45, 100-60
12 | M12 | 18 | 7 | 50-35, 80-55, 125-75
14 | M12 | 22 | 8 | 50-35, 80-55, 125-75, 200-120
18 | M16 | 28 | 10 | 63-45, 100-63, 160-100, 250-150
22 | M20 | 35 | 14 | 80-55, 125-85, 200-125
28 | M24 | 44 | 18 | 100-70, 160-110, 250-150

Worked example: 18 mm slot

An 18 mm slot takes DIN 787-18-M16. A 25 mm strap, a 6 mm DIN 6340-17 washer and a 24 mm DIN 6331 collar nut stack to 55 mm above the table. Add the slot neck height under the table top (often 25 to 30 mm on an 18 mm slot) and the 100 mm bolt with 63 mm of thread covers it, while the 63 mm bolt is too short.

DIN 787 bolt vs DIN 508 nut and DIN 6379 stud

DIN 787: one piece, quick, fixed length.
DIN 508 + DIN 6379: change studs for different clamp heights; the nut stays.

Common problems

Head too tall for a worn or shallow slot: check k against the undercut.
Nut bottoming on the shank: pick a longer b.
Undersized grade for heavy clamping: use 10.9 or 12.9.

FAQ

What is a DIN 787 T-slot bolt?

A forged bolt with a rectangular head that slides into a machine table T-slot. The head has milled flats so it cannot turn in the slot.

What is the difference between DIN 787 and DIN 508 plus DIN 6379?

DIN 787 is one piece with a fixed length. A DIN 508 nut with a DIN 6379 stud does the same job, but the stud can be changed for height.

Why are there two M12 sizes?

The 12 mm and 14 mm slots both use M12 thread; the 14 mm bolt has a bigger head (22 x 8 vs 18 x 7).

What grade are DIN 787 bolts?

Catalogs list 8.8, 10.9 and 12.9 steel, usually forged and blackened.

Why are 16, 20 and 24 mm slots missing?

One catalog sells bolts for these slots, but the other sources do not list them, so we left them out. The standard also has 5, 36, 42, 48 and 54 mm sizes that our sources do not dimension.

How is a DIN 787 bolt ordered?

By slot width, thread and length, for example DIN 787-18-M16-100.

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General shop information only — follow your drawing, tool maker's data and your quality system.