There were two main variations of the Thunderjet pilot seat. Published information states the first type was used up through the F-84E, the second type on the G-model. There seems to be some evidence that the second type was also used in the E-model (because it had the longer cockpit and therefore more room for the second type of seat which appears to be a little longer than the first type), but I don't yet have enough information to confirm or deny that evidence.
Illustration from the Republic archives courtesy of E.J. Boss.
F-84G Pilot Seat.