I have a brass steering wheel spider that is 11 1/2" across, Gail Roddas book says they are either 12 1/2" or 13 1/2" across.
Not sure if it's original, any thoughts,
It does not have the wood rim on it so not sure if one will fit.
I suppose it could be after market

The small ones are usually reproduction. Original spiders will have two key slots in the center hole. The reproductions usually have one. Look at one at Langs:

https://www.modeltford.com/item/3503B.aspx

I didn't see your post on this side. Earlier this morning I replied to your post in the classifieds, reposted here for convenience:

I've seen fractional variations amongst steering wheels, so I wouldn't hold anything to an 1/8th inch. Here is what I have handy to measure. When you hear steering wheel diameters, it's typically inclusive of the rim.

1910 14-1/8" rim (original) 12-3/8" spider, DB marked

1910 14-3/8" rim (reproduction) 12-1/2" spider, DB marked

1911 15-1/8" rim (original) 13-1/8" spider, DB marked

I've never been able to get a square answer from anyone as to the diameter of NRS steering wheels. Maybe they were a little smaller. There are reproduction wheels out there that are smaller than what I posted above. Does yours have the "Dodge Bros" mark on the underside of the hub?

No DB on the back.
One key slot

Yup, sounds like one of the little reproductions.