I know the nx5 pistons are no good; I always buy parts when cheap for motorcycles I wish to own in the future. I didn't mean to buy the kit ones though.
I did think the F3(89) pistons were a nf5 part number. Wasn't sure if they were different than the nf5 piston nf5 part number.
All adds to the excitement if they don't fit.
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mc18 F3, mc21 300, mc21ish sp, mc21/28ish.
cbr929, RC30, tdr250, rvf400, wave, gyro, joker.