hi, on my chevy i need to replace the big bolts on my doors, i have news hinges i'd like news bolt and the guy before me made a lot of bad things with french metric bolt ! in US hole !! Grrr !! hole are destroy, i'd like to put original one like this http://www.classicparts.com/1947-54-Door-Hinge-Bolt/productinfo/18%2D485/ , somebody know if it's UNC or UNF and wiche size , i need to rebuild the hole with a tap and i don't know wich one to order ! , Thanks ps: What is the most popular, UNC ? Thanks
The original bolts are 3/8-24 which is the fine thread. The metric bolt the PO probably used is just a tiny bit larger so running a 3/8-24 tap through now might leave the bolt a bit loose fitting. If you have the finish paint on the truck then replacing the cage nuts in the door pillar hinge pocket is probably not an option. The easiest thing would be to use a metric bolt with a 14mm hex head after chasing the threads with the correct metric tap. The 9/16 head on the factory bolt is so close to 14mm no one could tell the difference. You might have to shave the head down a bit thinner to match the factory look. The less desirable option is to tap the nuts out to 7/16, either fine or course, and use a "fairy head" bolt (no comment on it's sexuality) which has the hex head that takes the same wrench size as the threaded shank--in this case 3/8. The most common automotive use for these bolts are for steel tube exhaust headers. If you tap the cage nuts to a larger size use a very high quality and very sharp tap so the nuts don't twist in their cage, a real bummer.
