Replacement trem arm basics

scarry67

My partscaster Strat has a short arm which is now far from well-fitting. Taking seller's word for it, the bridge is USA model and the arm is about 5mm in diameter. Do push in arms work even on vintage type trems or do I need normal threaded arm? 

CasperCaster

@scarry67 the simple answer first - if it currently has a threaded arm then it will need a threaded arm as a replacement. If the current trem is genuine USA it will be Imperial - 3/16" diameter with a 10-32 thread, so this is what you need as a replacement. There are some 'virtual' drop in arms such as those for Callaham or Kev Hurley blocks, but they are partly threaded and work with a specific block which has a delrin/acetal/other synthetic material 'sleeve,' near the top of the threaded hole. With these blocks it is the sleeve which actually supports the arm, and the threads which stop the arm from falling out.

If the sellers information is not accurate, (or for others who find this thread looking for an answer to their own trem problems) there are a number of possibilities. As stated, vintage style threaded US blocks require a 3/16" diameter arm with a 10-32 thread. If it's a US vintage reissue trem it will have a steel block (test with a magnet), as will genuine vintage instruments except those from the 70's CBS era which have a zinc cast trem. String spacing and screw mounting for all of these trems will measure 56.4mm.

Many Mexican Fenders have a metric M5 threaded arm with corresponding block, as do many far eastern made Strats. Recent Mexican Fenders with modern narrow screw mounting and string spacing of 52.4mm have a zinc block stamped 'PW29' in the base, and an M5 arm. This trem is used on Mexican Std's, Roadhouse, Lonestar and other models. Note that I am not certain of the specs on the Mexican Classic Series, which may well be more vintage accurate. Also be aware that some far eastern made Strats/copies have M6 threaded arms and corresponding blocks. By looking at the screw mounting, string spacing, and testing the block material it is often possible to make an educated guess as to which replacement arm is required.

Finally, some US Fenders such as the second version of the Highway One models and the American Specials have a far eastern made trem built to Imperial-ish specifications. These trems are easy to identify as the screw mounting is vintage correct at 56.4mm, but the string spacing is the modern narrow spacing of 52.4mm and they have a steel block marked 'PW36' on the base. The arm on mine was 5mm, but turned down to 3/16" for the threaded part which was a 10-32 thread. So, in theory any US spec arm should work as a replacement on these models, but I haven't tried it myself.

So there you go - more than you ever wanted to know about Strat trem arms and blocks.....

scarry67

Blimey. Good to see Fender keeping it simple! Many thanks for info. Will seek USA one...