Pardal,
The following are my recommendations regarding rivets:
1. Understand the forces that will be imposed on the rivets during assembly and during actual use in the clutch. In order to properly specify the size, material, strength, etc., you need to know this.
2. You should become familiar with some rivet specifications. Mechanical fasteners like bolts, nuts, and rivets should be specified according to a product standard, which then also includes a material specification. Tubing is another product form that should be ordered this way. The product standards include a great deal of important information regarding dimensions/tolerances, mechanical property requirements, quality control methods, etc. Some relevant rivet specs to consider are:
DIN 7338 Rivets for brake linings and clutch linings
DIN 101 Rivets, Technical delivery conditions
JIS B 1213 Cold Headed Rivets
JIS B 1215 Semi-Tubular Rivets
ANSI/ASME B18.1.3M Metric Small Solid Rivets
ANSI/ASME B18.7.1M Metric General Purpose Semi-Tubular Rivets
3. Underhead fillet-- this is very important, as it influences the failure mode of the rivet. Any type of structural rivet should be formed (headed) not machined, but either process can produce rivets with too small an underhead fillet, which can cause premature failure. The DIN and JIS specs require an impact-type test to qualify the rivets, but the ANSI specs do not. GM4473P is an automotive spec for rivet ductility.
4. Most solid or semi-tubular rivets are cold formed from low-carbon, unalloyed steel wire. SAE grades like 1008, 1010, and 1020 are all used, depending on the ductility required for forming the part, and the strength needed in the final assembly. I suggest working with a company like Textron Fastening Systems when purchasing any type of fastener. They are not just a manufacturer-- they have a great deal of expertise in design, assembly strategies, and quality control.
I hope this was helpful, and good luck with your application.