I have a number of fully functional Boyce Moto-Meter Universal temperature gauges for sale.
Each is mounted on a nickel-plated dog-bone cap that fits a Pierce-Arrow radiator pipe,
Finding a cap that fits a P-A is extremely difficult, as most cars of the era had external threads on the radiator pipe, unlike the P-A cars.
I also have a number of caps with interesting / strange mascots attached, but the doge-bone caps are really the important aspect for P-A car owners.
I show one example here, but have quite a few others.
Prices vary, so be in touch if you have interest.