My FJ has crosshead screws securing the covers for its brake & clutch master cylinders. These tend to chew up. The brake isn't removed very often but the clutch is to keep the clutch pressure ok. The fluid in the clutch line tends to get dirty and also air seems to get into the system. I replaced the countersunk crosshead screws with stainless steel Allen (socket) head screws. The socket is very small (2.5mm) and tends to round in time. So I bought some stainless steel Pozidriv screws.
Phillips crossheads are designed to "cam out" to prevent overtightening. But this means that the head gets mashed up. Pozidriv are designed to provide greater torque. Pozidriv can be identified by the additional cross in the head. I mentioned Phillips but this get confusing here. Japanese use a different screw JIS (Japanese Industry Standard) B 1012. These can be identified by a punch mark on the head. These are suppose to be less likely to "cam out" than Phillips. The Pozidriv screwdriver is obviously different to the Phillips, the driver from a Jap bike toolkit look the same as Phillips to me.
The moral is always use the correct driver for the screw.
I got my screws from Triard (£1.69 for 25 pack, postage inc)
I usually use Tek
|Yamaha screw/Allen screw/Chewed up Allen screw (slot cut to remove with flat blade screwdriver)/Pozidriv screw|
|JIN screw punch mark for identification|
|Pozidriv bit (marked PZ2)/Phillips bit (marked PH2)/ Jap toolkit screwdriver|
|Chewed up 2.5mm Allen key|
|FJ clutch master cylinder with Allen screws|