Guide · Clamps, T-track and inserts
Threaded inserts for a CNC spoilboard: thread, wood and drill size
Pick the internal thread, then the insert family for your board, then the maker's drill. E-Z LOK and Carbide 3D drill sizes for M6, 1/4-20, 5/16-18 and M8.
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Short answer
Choose the internal thread first (match your clamps: M6, 1/4-20, 5/16-18 or M8), then the insert family made for your board's material, then drill exactly what that insert's maker lists. The same thread can need different drills: for M6, E-Z LOK lists 25/64, 23/64 or 21/64 inch depending on the insert.[1]
Step 1: the thread
The insert sets the thread every clamp bolt must match. Pick the thread your clamps, T-bolts and stops already use. If you are starting fresh, see M6 vs 1/4-20 spoilboard threads.
Step 2: the insert family for your board
E-Z LOK groups its E-Z Knife inserts under hard wood and its E-Z Hex and E-Z Fin inserts under soft wood.[2] Two examples in M6:
- E-Z Knife 400-M6 is brass with an M6-1.0 internal thread, made for hard woods such as oak, cherry and maple. It installs with a bolt and jam nut or the DT-M6 drive tool.[3]
- E-Z Hex 900610-13 is a flanged, hex-drive, zinc-alloy insert with an M6-1.0 internal thread, listed for soft woods including pine, composition board, MDF and plywood.[4]
If your spoilboard is MDF, the E-Z Hex part above is the family E-Z LOK names for it.
Carbide 3D sells its own threaded inserts in M6 x 1 and 1/4-20, 13 mm long with a 6 mm hex drive.[5] It does not state the material.
Step 3: the maker's drill
E-Z LOK's drill chart lists the drill per part number.[1]
| Thread | E-Z Knife (hard wood) | E-Z Hex (soft wood) | Finsert |
|---|---|---|---|
| 1/4-20 | 25/64 in | 23/64 in (10 and 13 mm) | 21/64 in (270-4-BR), 13/32 in (370-4-BR) |
| M6 x 1.0 | 25/64 in (400-M6) | 23/64 in (800610, 900610) | 21/64 in (270-M6-BR) |
| 5/16-18 | 33/64 in | 7/16 in | 13/32 in (370-5-BR) |
| M8 x 1.25 | 33/64 in | 7/16 in | 15/32 in (370-M8-BR) |
For 1/4-20, E-Z LOK lists 25/64 inch for E-Z Knife inserts and 23/64 inch for its 10 mm and 13 mm E-Z Hex inserts.[1] For M6, it lists 25/64 inch for the 400-M6 E-Z Knife, 23/64 inch for E-Z Hex 800610 and 900610, and 21/64 inch for the 270-M6-BR Finsert.[1] The 5/16-18 and M8 rows follow the same pattern with larger drills.[1]
Carbide 3D gives 9 mm (0.354 inch, letter T drill) as both the recommended and the maximum pilot hole for its inserts.[5] Do not mix one maker's drill with another maker's insert.
Picks that fit2 products
For M6 clamps in an MDF spoilboard, choose E-Z LOK 900610-13 (M6-1.0 x 13 mm flanged, 50 pack).
More on choosing
For 1/4-20 clamps, choose the EZ-901420-10 kit (10 flanged 1/4-20 E-Z Hex inserts with a drill and drive tool). Both are soft-wood inserts per E-Z LOK; not for hardwood boards.
M6 inserts for an MDF spoilboard
E-Z LOK E-Z Hex threaded insert for soft wood, flanged, M6‑1.0 x 13 mm (900610‑13), 50 pack
1/4-20 insert kit for soft wood
E-Z LOK E-Z Hex 1/4‑20 x 10 mm flanged insert installation kit for soft wood (EZ‑901420‑10)
Shorter inserts
Carbide 3D staff said 10 mm M6 inserts can be used instead of 13 mm inserts, but every bolt then needs to be 3 mm longer.[6] In the same thread, a community member (not staff) added a tip about keeping bolts from bottoming out in the insert. Check bolt length against the insert depth and your clamp before you tighten.
What we do not know
We found no pull-out rating for the 900610-13 on its part page. We publish no holding-force figure for any insert. If a job puts heavy sideways load on a clamp, ask the insert maker.
Next
Questions
What drill size for M6 inserts in MDF?
It depends on the insert. E-Z LOK lists its 900610 E-Z Hex insert for soft woods including MDF, with a 23/64 inch drill; Carbide 3D recommends a 9 mm pilot hole for its own M6 inserts.[4][1][5]
Brass or zinc inserts for a spoilboard?
E-Z LOK matches the insert family to the wood: its brass E-Z Knife 400-M6 is for hard woods such as oak, cherry and maple, and its zinc-alloy E-Z Hex 900610-13 is for soft woods including MDF and plywood.[3][4]
Can I use shorter inserts?
Carbide 3D staff said 10 mm M6 inserts can replace 13 mm ones, but every bolt then needs to be 3 mm longer.[6]
Does E-Z LOK publish a pull-out rating for these inserts?
We found none on the 900610-13 part page. We publish no holding-force figure.