The main apparatus

Five pieces make up the traditional studio, and every one of them does something the others do not.

Pilates apparatus and alternative names
ApparatusAlso calledWhat it does
ReformerSliding carriage with springs; widest repertoire
CadillacTrapeze tableFixed frame with overhead springs; best for rehab
TowerHalf CadillacVertical frame mounted to a reformer
Wunda chairPilates chair, low chairCompact; standing and pressing work
Ladder barrelDeep spinal extension and side-bending
Spine correctorStep barrelSupported extension, small footprint
ArcPilates arcLightweight curve; fits on a carriage

Why names vary

Some pieces have a traditional name and a descriptive one — Cadillac and trapeze table are the same thing. Others acquired manufacturer-specific names that entered general use.

When comparing equipment between suppliers, work from the description rather than the name. A "combo chair" from one maker and an "exo chair" from another may be near-identical products.

What a full studio has

A traditionally equipped studio has reformers, at least one Cadillac, a chair, a ladder barrel and a spine corrector. Modern group-class studios often have reformers only, sometimes with towers.

Neither is wrong — they serve different business models. A group-class studio does not need a Cadillac; a rehabilitation practice very much does.

What to buy in what order

Reformer first, always. Then a chair, which adds the most new repertoire per square foot. Then an arc or spine corrector. A Cadillac or ladder barrel only if you have a specific need and the floor space.