The metal protrusion on the bottom left pad is a wear sensor. That pad goes on the inside. When the pad becomes thin enough, the protrusion will rub against the rotor, indicating it's time for a change. Here's a YouTube video showing installation:

 

You're overthinking this- you have the right pads. Use the pads with the small "nipples" on the piston (inboard) side, and the "smooth" pads on the outboard side of your sliding calipers. Be sure to retract the caliper pistons with a C-clamp or large pair of channellock pliars before fitting the pads into the calipers. Most experienced DIYers have seen this type of brake design before, and now you'll join their ranks.

 

Thank you both for the quick response. The video from Karlh couldn't have answered it any better! Have to admit, did feel a little stupid after seeing it though. I was focusing on the protruded end thinking it was supposed to slide into something. Definitely overthinking it as DKmura mentioned.

Interestingly enough, stopped by two O'Reilly's and neither store new the answer. Remember when Auto Parts stores hired people who knew car repair...........

 

You're welcome and it's not surprising that the auto parts folks didn't have any answers for you. But cut 'em a break- with the pay/benefits they get, they may not have the best qualifications. Also, they're paid to move parts, not provide installation advise.

 

OK. Now the engineer in me is coming out....looking for a little education.

1. Why do the front brakes have wear detectors on the inside and outside and left and right and the rear only has it on the right rear? Is this because of all of the factors of alignment, turning, etc where each pad can theoretically wear differently and the back brakes on a fixed axis would wear uniformly?

2. Why is the wear indicator on the right rear vs the left rear?

3. Why is the wear indicator at the upper end of the pad? Is it because it is at the initiation point of the rotor and the pads where the highest wear would be expected to occur?

4. Regarding the front brake caliper guide pins, why does one have a seal around it and the other doesn't. Is this to create a pressure effect which could be uneven if it was on both bolts?

And now for one installation question:

Which front brake caliper guide pin goes on the top hole and which on the bottom hole?