The slit is large so these may not hold a manual brush securely without added duct tape to the handle. You may wish to purchase a tennis ball and cut a smaller slit yourself. There are also triangular slit or cross-slit designs available. I haven’t tried any of these pre-cut ones myself, just posting for ideas! You could potentially cut another hole as a new “top” that’s smaller/more secure and use the bottom hole to allow it to slide higher up on the brush for better grip.