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Old 09-17-2019, 08:30 PM   #1 (permalink)
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Default M2.5 Head Bolt

The Mini Protos M2 cross-bolt just does not cut it. This tiny little screw cannot develop enough clamping force from the head block onto the shaft, or worse, the threads strip.

My experience is that the block does clamp better to the hollow shaft than the solid shaft as the former seems to sping-back more, but still ultimately it does loosen.

I have seen later production hollow shafts and it appears to me that the shaft length above the cross-hole changed and is at the upper tolerance creating a tighter fit of the head block to the shaft even before the nut is locked-down. This must be due to the near-interference fit of the shaft to block bore depth. This coupled with the newer 380 sporting a M2.5 cross-bolt tells me MSH was aware of the problem.

But no worries, for it is very easy to dill-out the existing hole to accept a M2.5 bolt.


1. Place a little Locktite on the shaft and install the block and M2 bolt.
2. Let adhere, and remove bolt.
3. Fill cavity with oil (this will allow your HSS bit to go through like butter).
4. Drill with 2.40mm bit (my M2.5 bolt calipers at 2.38mm). Shown level here on a phone book (or block of wood).
5. Use M2.5 bolt (12.9 grade, 20mm) and some 0.75mm steel washers + locknut.
6. Now nice and tight.
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Last edited by FNFAL; 09-18-2019 at 11:58 AM..
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Old 09-18-2019, 10:30 AM   #2 (permalink)
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I've never been a great fan of this type of head fixing - I much prefer the clamping that you get with a J-bolt and 2 perpendicular bolts, but good work to improve the clamping effect
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Old 09-18-2019, 11:45 AM   #3 (permalink)
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Thanks Mike. Since I don't DFC, this was my only choice that I know of.
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Last edited by FNFAL; 09-18-2019 at 12:01 PM..
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