If you get a your sleeve or hand in there, it could be pretty rough on skin (or worse, if you get wrapped-up).

There are shaft collars (McMasters sells them). They have set screws that are recessed. I believe they are Ruland's : http://www.ruland.com/shaft-collars.asp?gclid=CITyy8qnhsUCFYEjgQodVXsA3A or http://www.ruland.com/ps_collars_shaft_sp_hex.asp http://www.mcmaster.com/#split-shaft-collars/=wub3aj (Stainless Steel, I would suggest)

PYI distributes them now (I don't know if they're the same as the ones form McMasters) http://www.pyiinc.com/?section=browse&action=product-detail&sku=07-SRC-134