If you are referring to a matched pair of long and short piece to make a properly length apex seal. That is how I expected to receive them but instead I got a little baggie with 6 long pieces and 6 short pieces. None of them marked to indicate a matched pair.

 

I have run into this issue before. I have measured several sets of stock apex seals and atkins and hurley ones. The stock length is usually 79.9 to 79.95 mm and the aftermarket ones generally 80mm and over with a larger variation than stock ones. I had one at 80.1 mm and it had to be sanded down as it would have expanded even more at high temps and there is not enough room at the cut of the seals to accomodate that much. Also, it is a myth that removing 0.05mm or so will greatly affect compression. If you look at 1st gen 13B service manual, the mazda spec on the length of the seal is 79.8mm. Quite a bit more clearance than the 2nd gen 3 piece seals and they worked just fine.

One more thing, the easiest way I found to measure the length was to put the 2 pieces of the apex seal on a magnet and then measure with a micrometer. No need to glue them.

 

I didn't clearance my atkins apex seals at all. Just threw them in. I've got a big side port/exhaust port and at 940 rpms, pull -400 vacuum. Not bad for just throwing them in.