This is a set of stepped washers designed for reducing a 14.1mm or 9/16″ hole in a flange for 12mm bolts. It allows the use of S14 front coilovers to mate up to any S13 style mount. This kit will also be applicable to all other rt.trackpro adapters designed for S13 coilovers.
Simply, the narrow side will insert into the S14 coilover mounting holes from the outside, shrinking the opening to the appropriate S13 size of 12mm. They will add approximately 3mm of thickness outside the bracket on each end, so in rare cases, longer bolts might be necessary, but the standard washers normally used could be omitted as well.
They might also be useful in other cases where a bracket has wallowed out a little too much for a 12mm bolt, for example a 1/2″ (12.7mm) hole, where a little tighter fit is required. In such a case, the hole could be re-drilled larger, to just over 14mm for use with these inserts. Note that insert depth is approximately .130-.135″, if used in thinner bracket material, some sanding or trimming may be required.