8 machined wheel spacers measuring 4.55 mm in thickness each that allow you to convert your Marwe 610's to hold our 105 mm wheels, which have 24.2 mm wide hubs. Total wheel assembly thickness then matches so forks aren't spread or pinched.

Doing the conversion is super easy. You need two 10 mm wrenches to slide out your axle, then put one of these wheel spacers on each side of the wheel between the forks, slide axle back through. 

To determined if you have Marwe 610xc or 620xc skate rollerskis, measure the wheelbase from center of axle to center of axle in mm, and that'll either be 610 or 620mm. 

If you have the aluminum Marwe 610a skate rollerskis, you'll want the conversion spacers for Marwe 620xc which also work on the 610a.