This Pair of No.663-R Fuse reducers install on fuse ends and permit smaller 30A 600V size fuses to be used in larger 60A 600V fuseholders. This reducer is for use with Class R Dimension Fuses including Edison ECNR/ECSR RK5 and LENRK/LESRK RK1, as well as Bussmann FRNR/FRSR RK5 and LPNRK/LPSRK RK1 and Gould TR/TRS RK5 and A2DR/A6DR RK1