I’m actually using a Onsrud 1/4" shank 1/8" diameter downshear in mine, at the moment. It’s a uniflute, which works quite nicely with the limited RPM control on the DeWalt. I use my 1/8" collet for leeeeeeeeetle bits, 1/32nd and soforth. I tend to prefer the largest shank diameter I can use for a given diameter, to help with bit stability.