I see them for sale on EBay, but most never list there thread size; will they fit the Chevrolet radiators?

Some will and some won't.

Some do some don’t I kind of figured that already

That is a question you will have to ask the seller. Just for information, the later 4-cylinders are all the same size. The 1928 is excluded as it has a large neck and even goes into the early 6-cylinders.

I wrote to Gary W. as he has the spare parts for some of the meters, and he sells new ones. Here is his explanation:

The hole (in the radiator cap)for the Jr. motor meter would be approx.7/16 inch and for the Sr. Motor Meter 21/32 inch.

The small motor meter (Jr.) was used on the 490's and up through 1928. The Sr. Motor meter was used on the Baby Grand. I have had a few of the Jr. motor meter nickel plate. They come chrome plated normally. To my knowledge, I am the only one doing this.

I measure several caps and the radiator threads them self's and come up with different sizes, but fairly close.

1914-27 1 & 670/1000 or about 1 5/8 inch
1928-30 2 & 670/1000 or about 2 5/8 inch


As far as I (Solan) know it impossible to get a spare thermometer only to the (old, used)junior meters. You must buy a complete new made.

If you want to buy an old meter on e-Bay, ask the seller to test the thermometer in hot water, and get the reply, before bidding. If no red color shows up after some few minutes, leave the bidding to others, as well as if the picture shows that the red is visible in the meter. (It might be possible to repair meters which have been laying on the side, but better to buy a "fresh" one.)

Good hunting, folks!

Here are some few links:
http://www.mascot-mania.co.uk/orphanage.html?/motometers.html&19orphan57

http://www.arteauto.com/index.asp?Category=31&PageAction=VIEWCATS

http://www.prewarbuick.com/features/reaching_the_boiling_point

http://www.lebaronbonney.com/osc/ca...;osCsid=ef234f010f4b3e7b893c1ad191d06dcd

Restorations:
Restoration Supply Company
2060 Palisade Drive
Reno, NV 89509
775/825-5663
E-mail: restoration@rsc.reno.nv.us
Remanufactured MotoMeters. Catalog of early car parts $2.50

Restorations/Ways of repair:
http://forums.aaca.org/ubbthreads.php/ubb/showflat/Number/389104

There are more links around, but hope this clarifies some of it.

Thanks Solan
That was the kind of information I was looking for.

Fine. Here is the link to: http://www.restorationstuff.com

On page 35: (You need Adobe)
http://www.restorationstuff.com/Catalog/RSC%20No23%20web3.pdf

they offer many meters and some parts.