5/32 drill bit size is the tightest tolerance size for 10-32. If you have a heavily coated fastener, a Friday fastener......... it may get tight. If you have a cheap fastener it may snap. #21 isn't hard to find out in town. I'd use 5/32 for aerospace level stuff with aerospace level fasteners if directed by spec. I'm not sure I'd trust a non sourced fastener for this.