BOX Three Prime 9 eBike Cassette - 9-Speed 12-50t BlackBOX Three Prime 9 eBike Cassette 9 Speed 12 50t Black. The Box Three Prime 9 cassette is a great all around cassette option. All cogs are stamped from steel and subsequently the larger ones are pinned to alloy spiders. It also features weight reducing holes on the cogs. The Box Three Prime 9 offers ultra wide ratio with consistent progressions Prime 9 technology offers the same range as a 12 speed drivetrain with fewer gears to shift through Fewer