Lots of folks, including myself, have tried to use guitar winders on mandolins. They don't work well at all. So it is not uncommon to try and modify guitar winders to fit. I cut the side off a cheap plastic one with a hacksaw, then glued it back on after I'd shaved it down enough material. It worked, but it was butt ugly.

If you want to buy one, The Mandolin Store has some nice wooden ones for $20. They look nice, and they work. The one that Darylcrisp posted is a very good choice. They're cheap, they work, and they won't scratch your mandolin. What else you want.?

But be careful with cranks, you can bend you tuners if you put enough torque on them. Which is one of the reasons I bought a Frank's Crank. They are slightly offset to mimic the rotation of the wrist, and in theory, that should put less pressure on the tuners. No one needs that expensive of a winder, but they are a joy to use.