The Avid B7 3.5x50 Rear Inner Hardened Hinge Pins are made from, you guessed it, hardened steel. Kit hinge pins are 49.5 and are just a tad short which aids in them ripping out the side of your kit C arm mount. The added length will help prevent this from happening.
Darren, our UK distributor (Xfactory), brought this product idea to our attention when the B7 came out. He also said for the original C arm mounts with the pill cutout, that you could flip them and remove a 1mm shim from your arm spacing so there was more material to keep the hinge pin from pulling out. Great information over there in the UK!