by MMStingray54 » Tue Jan 14, 2020 3:20 am
People talking about basses - excellent!!
To expand on what Jim has said, it's called a tug bar. Introduced on the 51 Precision as a piece of maple held on by one screw, it gravitated to a plastic bar held on by two screws in early 57 (when the Precision changed from a telecaster shape with huge pickguard to more of a Strat shape). It also appeared on the Jazz Bass from the start. This enabled people to 'tug' at it with their fingers whilst striking the strings with their thumb - which few bass players actually did, using either a pick or their finger(s) to play (eg James Jamerson - allegedly one finger).
However it took Fender until 74 (Jazz) and 73 (Precision) to move said bar to above the E string enabling finger style players to plant their thumb on it and pluck with their fingers - the original position having confused many a young player and been used by very few, this new position appeared to have some purpose - however not only could the new position impede pick players, it could certainly cause a bruised thumb for the burgeoning thumb slap player, a style which was taking off at the same time in R and B (early Rose Royce, Sly and the Family Stone and many others). Fender deleted it around 1983 with the American Standard and other new versions - although it has remained on reissues.
It's sort of part of the 'furniture' on vintage Fender basses and reissues!