Likely a metric threaded screw (M2 or M3). Computers use M3 x 5mm metric screws for attaching DVD/CD drives within computer cases.
The M3 size in 6 mm length can be found at and Ace or other hardware stores
that has the Hillman small parts drawers.http://www.hillmangroup.com/locations.html
Good hobby shops have these smaller metric screws. eBay and Amazon are filled with suppliers.
MTS - http://www.angelfire.com/biz2/mts/Icom IC-251
The IC-251 is basically a more advanced version of the IC-211.
The Main unit is almost the same. The PLL and Logic are very different.
The biggest issue with the 251 is the CMOS logic. It "glitches" and is very static sensitive.
The CPU and Expander are no longer available new.
This Icom radio model is generally it is very reliable, and needs very little maintenance.http://www.angelfire.com/biz2/mts/Oldies.html