The BL units with a "X" designation like the BL58X is a Garrett GT small-frame based unit (Garrett GT/GTX30 & GT/GTX35). These BL-X units all come standard with billet compressor wheels but are Dual Ball Bearing only. Just like with the Garrett GT30's and 35's, water cooling is required. The BL-X units are direct fit for turbo kits that use Garrett GTX30 & GTX35 turbos.