Does anyone know if the metal insert portion of a Fiat spider seat belt is a universal size? I want to replace the 12" or 13" inch portion of the seat belt with the red button that hooks to the drive shaft tunnel. I see a lot of black cable, red button, buckles that appear to be about the right size for sale. no need to replace the belts with a whole new system as they are in good shape. I don't want to purchase a new buckle piece not have the bucle work.

The old red button portion of the belt has some caked on grime almost like battery acid that I have not been able to get off the buckles. Seems like a quick and inexpesive fix that will look good. Thoughts?

I don't think it's universal. You may find another car that uses the same one as a Spider, but I know there are a lot of different designs out there. Maybe some Euro cars used the same ones?

As Csaba mentioned the metal male part of the seat belt buckle mechanism is somewhat unique. So I traced the metal insert part and compared it to some of the other vehicles at the house. Suburban, Honda, BMW, Ford. The Fiat buckle shares some measurements with each type.... It does not share all the measurements with any one type. It looks like anything really close to exterior 35 mm X 23mm and interior 20mm X 10mm may work with the existing buckle. At some point I'll disconnect the belt and take it to a salvage yard to see what works. The universal belts look to fall in a potential range given the similarities between various OEM measurements. I'll post if i find something that works that is inexpensive. This way if someone needs to only replace part of a seat belt they can potnetially still use the other half.