We have a vast finished ground flat stock / gauge plate range both in terms of sizes stocked in metric and imperial.
Gauge plate is a high carbon steel ground to thickness and sometimes, but not always, to height. Tolerance on thickness is generally around +/-0.001". The important feature of gauge plate, indicated by high carbon content, is that it can be hardened and tempered by relatively simple means (compared to HSS). Hence it can be machined soft, and then hardened and tempered to produce cutting tools, springs etc.