This might be a stupid question, but what are thumb rests for? I don't know how you would put your thumb where they are usually located and play? I can find tons of basses with them but can't find anyone using one.
You could searchbar this, this question has been asked a couple times in the last few weeks.

Anyways, history lesson: When Leo Fender brought the Precision bass to market in 1951, it was the first widely available electric bass guitar, so Fender had to entice upright players to make the switch to the new bass guitar. Some upright players plucked with their thumbs, so the thumb rest, or "tug bar" was added to give players something to anchor their fingers with while they plucked with their thumb. Nowadays its more a cosmetic detail to make basses look more vintage-y.
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Spector and Markbass
well, it was on the first electric bass made because it was based off of an upright, most upright players rest their thumb on the fingerboard and thus the thumb rest was designed. ive seen them on both sides of the body which is weird to me, but i assume some people used to play with their thumb and anchored their hand on the rest. well, if i rested my thumb at all id love a thumb rest. but since i dont, it would just be an aesthetic thing, which is usually the case nowadays.


DOUBLEEDIT: you beat me to the punch....im a failure.
My name is Greg, use it.



there is a difference between a thumb rest and a tug bar. both are commonly called a thumbrest though.
no sir away a papaya war is on