There are two types of gage blocks, the rectangular Jo blocks, and the less common square Hoke blocks; both types have their advantages and disadvantages; the Jo blocks may fit into spaces provided in some fixtures such as sine fixtures that Hoke blocks will not fit into, Hoke blocks have the advantage of being held together by a screw device through an axial hole in their center that is countersunk for a flat head screw. In that way, tall stacks of blocks may be made up easily without the tendency to fall apart, and all the accessories are held on in that manner. There are clamp devices for Jo blocks as well, but the Hoke setup seems easier to deal with. Of course, the Jo blocks were named for C.E. Johanssen, and the Hoke blocks were designed by Colonel Hoke of the U.S. Army, in charge of war production quality control during world war one.
I see 86 piece sets of Jo blocks on e bay (used) for around $250; who knows how they would calibrate, but how good do they need to be for hobby work? I have both types with accessories, but very rarely use them.