I purchased a set of rear pads (PN AP 332) from Porterfield at the below link a few weeks back.
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Everything was going great, pads seemed to lock into the caliper fine, the piston was fully spun in/retracted... and then...
When I attempted to install them on the car, I couldn't fit the caliper back on over a brand new Stoptech slotted rotor (PN 126.45052SL) from J-Auto.

Confused, I went ahead and measured the thickness of each component:
2x R4-S Brake Pads w/ backing plates: 35 mm (not sure what OE pads are?)
Rotor: 20.13 mm (owners manual states this is acceptable)

This yields a total thickness of 55.13 mm

Measuring the actual spread of the caliper (casting edge to casting edge):
48.5 mm

This means the pads are over 6 mm too thick!

Anyone have an idea what is going on here? Am I just an idiot?
My next step is to contact Porterfield to see what they have to say...

 

I've used R4-S in the rears for ages and never run into this problem before. Will they clear if you remove the backing plates? Could be a bad batch I guess...

 

Just got off the phone with Porterfield, looks like they sent the wrong pads, they are supposed to be 13.1 mm thick per pad, the ones I have sitting here are 17.5 mm thick.