MC18 magteks are 18" rear not 17", and MC28 should be self explanatory, MC18 and MC21 rears will not fit MC28, all fronts are interchangeable. If you are looking at MC28 magteks you are obviously aware that the rear is a different fitment to the others, apart from that and the MC18 rear being 18", which you don't want, no visible difference.
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