What size are CAT block tyres?
 

I remember using them 20 years ago on an Optima (2" wheels I think) on a normally slippy Tarmac /grass track and they were the only thing that worked and didn't wear out in 5 seconds. Now I want some wheels ( fronts all round) for 12mm hex, is there such a thing or are they 2.2" now?

2", they stretch to fit 2.2" wheels.
Looks to be the same mould from the olden days.

They are a pain to get on 2.2" wheels, lots of people cut off the inner rib on the wheel to make it sit a little better. They work great on track though.

So there's no 2" 12mm hex wheels about these days other than vintage?

No 5 spokes either, even in 2.2 :-( Not that i can find anyway.

They are 2" and are a pain to fit on new rims. I've heard people turn the tyres inside out and cut one of the beads off, I couldn't bear to butcher them.

I use yellow blocks on a bmax4iii on Tarmac for fun/practice. Love the fact they're 2.0 inches as I don't have to glue them! Tight fit on a 2.2 but no biggy.

Both tyre walls overhang the sides of the wheels so just check they don't rub on full lock.

Tamiya still sell 2" wheels from their rerelease buggies.
Manta Ray dish wheels part no. 0335102
Egress spoked wheels part no. 9335066

If you are feeling rich, Pargu sells plenty of alloy wheels in 2"
http://www.pargustore.com/alloy-wheels.html

It's also easy to find plenty of old wheels.

JC Racing sells several 5 spokes, intended for vintage racers but the various wheel fitments are used on most modern cars.
http://www.jcracingproducts.co.uk/clearance

HPI still make their Super Star rear wheels for the Super RS4 http://hpiracing.world/en/part/3031
Tamiya make their Star Dish wheels
https://www.tamiyausa.com/search.php?q=star+dish