A quick work of caution on the Bearing Boys blue wheels that are linked a couple of posts up. They do not have a plain bore centre, instead they have a roller bearing pressed into them which makes them no good for fitting on to the drill motor/gearbox output shaft. (Yes, I bought some without checking ). You could press the bearing out but the bore you are left with is bigger than the O/D of the typical 3/8UNF nut, so still not straight forward.

Bearing boys do a grey wheel which does have a plain bore that a 3/8UNF nut can be inserted/melted into. They feel about the same level of grip as the blue wheels, but I have nothing to confirm this.

Also as noted both the blue wheels and the grey wheels are heavy, but feel reasonably sturdy. I got some nylon wheels from them and screwed mountain bike tyre on to the outside and saved around 300g for a pair of 4" wheels.