Hi Paul

The steady is made out of 10mm steel I was going to add a piece about 25mmwide at 90degrees for strength but I havent found it needed it. Regards the opening I find it easier to put in place with the gap I've used it on 39 inch by 30mm croquet mallet handles 600long weedpots held in chuck and deep vessels it can be put in place without loosing true centre, and I use it when drilling through for table lamps.

Cheers Tony