Will it fit your mini grinder?

Probably not, I made it for my mini grinder to transform it in a micro router. I still have to design the lower part that touches the part I will be routing in, upgrades on the way as I design them, print them and test them.

How to fit it to any mini grinder tool like a Dremel?

By trial and error, you can before slicing to tweak it a bit by scaling it, so I recommend you print one with 20% infill, or less, and see ho it fits, if too largeat the chuck collar, resize it by the percentage you calculate to fit, same for the body collar. If the proportion of the collars is not as per mine router, than resize it to fit the largest (in percentage) colar tight, and in the gap remaining around the other collar, fit some thick rubber strip to give it a grip when tightening the bolts.

Same way you can play around with the vertical scaling.

The revolution in design is made not at 180 degees per half handle, but at 175 degrees for the half handle, so that there will always be a small gap between collars to improve grip, when bolts are tightened, I do not expect the two halves to touch at the collars, but to have good grip around the tool. however at the extreme ends, at the handles, is better if the oval shaped peices have no gap on the touch line, for your skin safety.

Once reached the right size for you, print a set with 100% infil, preferably PETG or PLA, Nylon but not ABS or HIPS, and not carbon fiber, makes it too stiff and brittle, and a bit of elasticity you need it by design.

Oh, before I forget, always print two of them, they work in pair... lol.

I placed two options here, vertical standing and horizontal standing on the print bed, your choice how to print them, I did it vertically for my reasons.

I always print tools at 100% infill, 120% flow and the layer width larger than the nozzle (.4 mm nozzle I print it at.5 width and .3 height) at the hoter end of that material, to improve adhesion, eliminate air micro gaps, make the part more resistant in use, and yes, that generates stringing, ut I set my slicer to comb inside over the infill, so some of it is taken care of it this way.