So, the Breakout 21x3.5” wheel has One Inch wheel bearings. And this Springer is a ¾” Axel. I found some Reducers. They are listed 25mm to ¾” and Also listed 1” to 3:4” Wheel Bearing Spacer. Yeah, bought them on eBay. Dumb. Really Dumb. I bought both (I didn’t know if I had 1” or 25mm Axel) and Both sets came. Same part#. And,.. uhhh,.... No they Don’t fit. I put a sanding wheel on my hand grinder. Then, put the spacer on a Socket Extension (so it can Spin) then surfaced it a bit.