Rivet hole size is min+0.1, max+0.2, the total thickness of the workpiece is generally the rivet length 45%-65%, it is best not more than 60%. Too short length is also trouble. For example, if the total thickness of 2 or more workpieces is 6mm, then the Aluminum Rivet length you select should be 9.23-13.3mm. In addition to the 6.4, 6.6 diameter, the other is to be able to pull the 6.4 and some of the gun can be pulled. Generally there are more in foreign, but expensive. The appearance basically no difference, but there has big difference between parts, the bad one will be not pulled tens of thousands of air leaking, a leakage effect is not good. Part is cheap, but changing is too much trouble. If you use, we suggest you to buy from well-known Rivet Manufacturer.