If the sealing surface of your short nose crank has any damage, this speedy sleeve taps in place and allows the installation of the original seal.
This is to suit the 1.6 SHORT NOSE crank which is found on 89-91 MX5's
It's hard to pinpoint the exact date of when Mazda switched to the long nose motor so it is best to look at the front harmonic balancer
4 notches (cut outs) in pulley = Short Nose
8 notches (cut outs) in pulley = Long Nose