Power Plugs for Nitro car and truck engines! HPI Power Plugs use a unique blend of platinum and iridium metals to produce a range of quality glow plugs that is suitable for hobbyists and racers. Recommended Power Plugs for HPI engines #1502 Medium R3 - 12R XS #1503 Medium Cold R4 - 21BB/S-25 #1504 Cold R5 - All HPI .15 engines (T-15, 15FE, etc.)