Fixed Axle Sleeves
These fit any yo-yo that normally uses a C sized bearing and transform it into a fixed axle yo-yo. You should always use cotton strings with them and change your strings at reasonable intervals to prevent damage to the yo-yo. $2 for flat ones and $5 for grooved ones.
Wooden Caps
These fit Freehand Zeros and any other yo-yo that can use FHZ sized caps (such as the Duncan MG and Werrd Hour). $5 gets you a pair of these. Custom designs can also be added on a case by case basis, but must be kept fairly simple (PM me and we can talk).
All sales include free shipping. Quantities are limited so they are first come first served. Once I run out of stock, I will edit this post and all orders will be put on a waiting list.
It’s a wooden sleeve that fits over the axle in place of a bearing, thus making your yoyo a fixed axle as Mr. Yoyoguy says above. See the picture mrcnja posted.
It really depends on the yo-yo. Throws that use thin card stock caps like the FH2 won’t be good candidates. Some of my YoYoJams look like they would be a possibility, while others do not. What yo-yos in particular did you have in mind?