Sounds like Inland is wrong, plain and simple. I've never installed a 2 or a 4 millimeter thick plate, much less held one in my hand. If I ordered a 4, I expect a 4, and it is not my responsibility to recognize it or mic it when it gets here. If I order 13.5 - 1 pistons for a motor and I receive 12.0-1 pistons, is that my fault? Hell no. It sucks for them that the spacer was port matched and is now a paperweight, but they need to accept the return. That's just the cost of doing business and making a mistake.
Keep on keepin on man....post this EVERYWHERE