Not sure my reply/post was all that clear, by re-tapping to M5, standard pitch at 0,8m/m and using bright zinc countersunk head fastener suitable length ( used a lot in electronics trade ) was much quicker than procuring suitable fasteners and ditto Oring in Australia. There were specialty fastener supply houses that i could have used in the day. Would not use black passivated screws ( usually high tensile ) for the mod. Not a fan of plated HT fasteners either just quickly, given what i know about electroplating, though is found in the engineering trades.
*** Assume that the M4.5 by 0,75 is drilled at M4.5 minus the 0,75m/m pitch equals 3,75m/m for standard metric major minor thread form. The M5 option will drill at 4.2m/m Allowing a reasonable new effective M5 thread form, not perfect though will work for moderate torque, and perhaps at least 2D+ thread engagement.
Have box kits of Orings here, in the hundreds of individual Orings, re-machine of the groove was done with correct groove form as per Oring manufacturer engineering data on depth and width, as i recall that groove to Oring form on Dellorto is outside these guidelines for groove and Oring reduction of compression set failure ( common on many instances of "failed Oring" finger pointing ), there may well be reason for this at Dellorto, know if your careless the thin Oring traps ( despite chamfer on carb body ) and is damaged at installtion time on the fitted to engine carbies. j
