This reduces the clearance between the frame and the rotating tether spool to ~1mm. This only slightly increases the friction, making it slightly louder when turning the handle to wind up tether .

But for both the slim and standard tethers, this is worth it! I've always struggled with slack tether finding its way into this gap, and it can be difficult to remove especially in the middle of an ROV operation! Banish those problems for good. 

Required hardware - 2x M3 screws per guard

Position guards so that rounded corners face the outside of the spool frame.