An upholstery regulator is an upholstery

Upholstery

Upholstery is the work of providing furniture, especially seats, with padding, springs, webbing, and fabric or leather covers. The word upholstery comes from the Middle English word upholder, which referred to a tradesman who held up his goods. The term is equally applicable to domestic,...

 tool

Tool

A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...

 which smooths irregularities in the stuffing beneath the coverings.

Whilst it looks similar to a needle it is heavier; like needles the regulator comes in various gauges and lengths. It is used to poke through the various layers to adjust the stuffing before the final cover is put in place.

A related tool is the stuffing iron, which is used to push the stuffing into the curves and corners of a piece of furniture; it has a narrow piece of steel with one toothed edge to grab loose stuffing and place it in the hard to reach spots.