I have a DLE-30 engine on aWild Hare Hobby baby Extra 260. I bought a MPI 3" spinner from Troy Built Models that had a 6mm prop nut that a 4mmspinner bolt attaches to. The problem is the hole in the propelor shaft of the DLE-30 is 5mm and they don't make a 5mm prop nut. I could just put a 5mm bolt thru the end of thespinner and bolt it down, but the head of the bolt won't fit into the recessed end on the spinner. Any suggestions on how anyone has mounted a spinner on the DLE-30.

Not sure if it will help you but I had a similar problem with a saito 125 on a TF P51. I put the bolt in my cordless drill (threaded end carefully) and with it turning took my dremel to the head of the bolt with a sanding drum. with both parts turning you can sand down the edge of the head so it will fit into the recessed hole in the spinner while keeping the bolt nice and round.

Welcome to the site.

I just use my grinder and grind the head of the bolt down on it's sides until it fits the spinner. I hold it by hand and have some nice cold water close to hand.