I didn't measure it, but I think it's about 2.5" or something. A fair sized spinner. I noticed on many of the full scale planes, they have tiny spinners.

Thanks, I try hard on the cowls. I find they can make or break a plane. I've certainly messed up my fair share. I just really take my time because I think it's a very important step.

I've learned to use overhead projector transparencies to help make a nice clean cutout. And a dremel of course. In this case, I mounted the engine with the drive washer being 105mm from the firewall, as specified in the instruction. Then I removed it, and mounted the cowl, and measured 103mm to the firewall. That roughly sets the "depth" of the cowl on the fuse. I put tape around the fuse with one edge flush with the edge of the cowl, and remove the cowl. Then, cut out a square of transparency, and tape it to the fuse so that the rear edge is butting up against the tape I laid down earlier. Now it's at the same depth as the cowl. Then I marked the red/white transision on the fuse covering, on the transparency, to get my vertical spacing.

Now mount the engine, mark the transparency, cut it out, check the fit around the head. Remove the transparency, and tape it to the cowl so the rear edges line up, and the red/white transision line matches the cowl. Then go ahead and cut it out. This was my best attempt yet.

See the tape I have laid on the fuse in the photos? With the black line? The black lines are exactly 5cm long, with the front end being exactly where I want my hole in the fuse. Now when I reinstall the cowl, I can measure forward 5cm from the back of the line, and hit my target fuse mounting point dead on. Stops from guessing where I should drill the cowl to hit the fuse point.