Proprietary dimensions and spline for use only with Surly Mr. Whirly cranks
3 types:
Short; to fit 68 and 73mm BB shells :BBSUWA68
Long; to fit 100mm BB shells e.g. Pugsley with 17.5mm offset: BBSUWA10
XL; to fit 100mm BB shells but for Moonlander with 28mm Offset, spindle length 171mm: BBSUWA71