Lightsaber Blade Retention Screw Sizes: M3, M4, 8-32 and How to Tell Them Apart
How to identify the blade retention screw in your saber, a thread size reference table, and why M4 and 8-32 screws get mixed up.
Short answer
Most sabers hold the blade with a small set screw or thumb screw in the blade holder, commonly M3, M4 or 8-32. Measure the thread diameter with calipers and count the pitch: M4 and 8-32 are almost the same diameter but have different pitches, so the wrong one will start and then bind. Never force it.
Lose your blade screw and the saber is useless until you find the right one. Here is how to get the right replacement first time.
Thread size reference
| Thread | Diameter | Pitch | Notes |
|---|---|---|---|
| M3 | 3.00 mm | 0.50 mm | Common in slimmer and budget hilts |
| M4 | 4.00 mm | 0.70 mm | Very common |
| M5 | 5.00 mm | 0.80 mm | Larger hilts |
| 6-32 UNC | 3.51 mm (0.138 in) | 32 threads/in (0.79 mm) | Mostly US-made parts |
| 8-32 UNC | 4.17 mm (0.164 in) | 32 threads/in (0.79 mm) | Common in US-made hilts; easily confused with M4 |
| 10-32 UNF | 4.83 mm (0.190 in) | 32 threads/in (0.79 mm) | Some US-made hilts |
These are the standard thread dimensions. Which one your hilt uses depends on the maker and sometimes on the hilt model, so measure.
How to identify your screw
- Measure the outside diameter of the thread with calipers. Round to the nearest size above.
- Check the pitch. A thread pitch gauge is cheapest. Without one, lay the screw on a ruler: an M4 has about 7 crests in 5 mm; an 8-32 has about 6.3.
- Measure the length. Too long and it presses into the blade; too short and it won’t hold.
- Note the head: thumb screw, hex socket (grub) or slotted.
No screw to measure? Use the hilt’s listing or ask the seller, then buy a small mixed kit so you have spares.
Why M4 and 8-32 get mixed up
They differ by less than 0.2 mm in diameter. An 8-32 screw will start in an M4 hole, then tighten suddenly after a turn or two as the threads fight. Forcing it strips the blade holder’s thread, which is a much worse repair.
Tightening
Tighten until the blade can’t move, then stop. For dueling sabers, check the screw before each session; impacts loosen it.
Questions people ask
What size is a lightsaber blade screw?
It depends on the hilt. M3, M4 and 8-32 are common; some hilts use M5 or 10-32. Check the listing or measure the screw's thread diameter and pitch.
Can I use an 8-32 screw in an M4 hole?
No. They are almost the same diameter (4.17 mm vs 4.0 mm) but the thread pitch differs, so the screw will start, then bind and can strip the thread in the blade holder.
How tight should the blade screw be?
Snug enough that the blade can't slide or rotate, and no tighter. Over-tightening can crack the blade wall or dent it, which can break a neopixel blade's strips.