Question

machines that use abrasive wheels must have safety guards protecting all these parts except: spindle end nut flange projections adjustable tongue

Explanation:

In machines with abrasive wheels, safety guards protect the spindle end, nut, and flange projections to prevent contact and injury. The adjustable tongue is not a part that requires such protection as it is designed to guide work - pieces and is usually accessible for adjustment.

Answer:

Adjustable tongue