Are you only expecting one person to reply, Carl?
**LINK** 
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The general wisdom is that slitting saws are safer without keys.
However; if you run them that way, the retaining screw/nut can tighten up … So remember to include spanner flats or a cross-hole on the arbor. … I write from bitter experience with a small [1/4" bore] saw.
MichaelG.