BAN005 torx convex head Ducati 0,9mm

0.9 mm as a step in its own right

0.9 mm is sometimes overlooked between 0.8 mm and a full millimeter, and yet it is a separate and commonly available size. The difference from its neighbors is only a tenth, but on a repeated assembly of heads it adds up: twelve pieces in a circle make a visibly different pattern from twelve pieces a tenth smaller, because the spacing between them changes as well.

The circle around a cover

The most common use is exactly the circular assembly. A clutch cover, an alternator cover or an exhaust flange is held by a ring of screws whose head shape is, on a finished model, one of the few places where handwork shows. Domed crowns at a regular spacing catch the light one after another, so the circle lights up and goes out as the model is turned – an effect flat printing will never give.

Layout and tool

The spacing is laid out most easily with a paper template stuck onto the part, into which the holes are marked with a needle. Drilling is done with 0.8 mm and always only after the filler has cured, otherwise the bit will tear the edge. At this size tightening with a tip is already possible, but with feeling, because the star hole is shallow and overturning rolls it out.

Worked out to reality, 0.9 mm matches a head of around eleven millimeters in 1:12 scale, or eight millimeters in 1:9 scale. Both are ordinary sizes on engine covers.

For a whole build it is good to keep to one shape of head and to tell the parts of the model apart by size alone. Alternating profiles without reason looks restless and on a competition table it catches the eye sooner than a missing part.