The 727 nut is a 5/8-18 right handed jam nut used as a fastener with Burr King 701 bearing. 

Often used with the 726 spring washer, the 727 nut only needs minimal torque to secure the wheel securely to the shaft.

As a rule of thumb a 1/8 turn past snug is more than sufficient to secure the wheel to the shaft. Over tightening will cause damage to the spring washer and possibly the bearing.