[Model "A" Fords]

Morse taper drills and reamers hold the torque with no fastener. The tool is slid in the taper using a quick hand thrust and works as long as the variables are correct. Tapers must be defect free or can produce a poor fit leaving the tool to depend on the tang if there is one. The taper is further tightened by the pressure caused from tool use and requires a drift to remove it. There are many twisted tangs on tools that had poor engagement because of a damaged taper surface.

The axel isn't loaded with a force from one end like above but from multiple directions, some pulling the taper apart. It has to be a nice fit using the nut to keep it engaged and a key for additional safety.

A loose fastener can expand and contract with the load causing fatigue. If too tight it can be over stressed and break. Designed correctly, the fastener will be torqued and pre-stretch to a point where the load during use stays below that set amount to reduce fatigue.

Of coarse what to do becomes a chore dealing with vintage parts with no history, hence the varied recommendations here using the trial and error method which appears apparently largely successful.