Definition
A class of mechanical fit between two mating parts in which the parts assemble easily by hand, with enough clearance between them to allow free relative movement or rotation without binding. Free fits are used where accuracy of alignment is not critical and where the parts must move or be assembled and disassembled readily.
Plain English
A loose, easy fit between two parts. They slide or turn against each other without sticking, and you can put them together by hand without forcing anything.
Context Anchor
Seen in aircraft maintenance when checking how pins, bolts, bushings, bearings, or other fitted parts go together and move.
Derivation
Free here means unrestricted -- the parts move freely against each other. It contrasts with tighter classes such as press fit or interference fit, where the parts are forced together and held by friction.
Why Pilots Care
Pilots who do their own preflight or owner-assisted maintenance will see fit classes called out in maintenance documents. Knowing the difference matters because using the wrong fit -- a free fit where a tight fit was specified, or vice versa -- can cause a part to wear quickly, vibrate loose, or fail to seat correctly.
Intuition Check
Free fit does not mean careless, sloppy, or free of cost. It means a controlled amount of space between parts so they can go together and move without force.
Example Sentence 1
The maintenance manual specified a free fit for the control cable pulley on its shaft so it could rotate without drag.
Example Sentence 2
During preflight, the pilot confirmed the throttle linkage had a free fit and moved smoothly through its full range.