Took a look at the Bill of Materials for the R-cars and a "1/4-20 washer 354610-S40" is called out for the axle-limiting cables. A check with AMK's catalog of Ford part numbers gives the specs as .250" id, .563" OD, .078" thick steel with S40 being Zinc. In reality, this is not a traditional 1/4-20 washer but a thick version of a 3/16 washer which is nominally .050 thick. AMK does not list stock on the Ford p/n.