One of my favourite seat rails for the mx5/miata. Reason being they have enough adjustment to allow the seat to be in a non bolt up right position. We in-fact use these on our own cars!
Here's what Skid Nation had to say about them:
Developed specifically for MX-5 with optimised lightweight construction – just 1.8 kg per set of mounts while still compliant with FIA requirements. By offering 36 available seat positions these will enable you to sit safely and comfortably regardless of your height.
Designed for use with the existing seat mounting holes, made from 3 mm structural steel. Finished in scratch-resistant matt black powder coating.
Set for one seat, compatible with all 1989-2005 cars. Successfully fitted seats:
Bimarco Cobra 2
Bride Zeta i-iii
Cobra Monaco (incl. Pro and Sport)
Corbeau Club Sport
Lotus / Tillett B5
Mirco RS1 3D
Sparco Grid 2 (requires cutting off a bit from the mounts)
Does NOT fit without fabrication:
Recaro Pole Position
Sparco EVO II
Sparco Sprint L
Has holes to accommodate NB/NBFL seat belt mount (depending on your seat, attaching the seat mount might require additional fabrication). Not required for NA (Mk1).
On NB (Mk2) and NBFL (Mk2.5) cars the left side (UK passenger side, EU/US driver side) has a bump on the transmission tunnel that requires flattening – can be done with a hammer and will not cause any issues with the exhaust.