Definition
A precision fit between two mating parts in which the hole has been finished with a reamer to produce a smooth, accurately sized bore that matches a specified shaft or pin diameter within close tolerance.
Plain English
A hole that has been finished with a special cutting tool so a shaft, pin, or bolt slides into it with an exact, snug fit — not loose, not forced.
Context Anchor
Seen in aircraft engine and airframe maintenance instructions when a hole must be finished accurately before a fastener or fitted part is installed.
Derivation
From the Old English 'ryman,' meaning 'to widen' or 'make room.' A reamer is a rotating cutting tool that enlarges and smooths an existing hole to a precise diameter — so a 'reamed fit' is one produced by that finishing process.
Why Pilots Care
Reamed fits are used where alignment and tightness matter — engine case dowels, control hinge bushings, propeller bolts. A loose or sloppy hole in these locations can lead to vibration, wear, or component failure, so the fit must be exact.
Intuition Check
Do not read fit here as simply “it goes in.” A reamed fit means the hole has been precisely finished so the part fits within the allowed limits.
Example Sentence 1
The dowel pins locating the engine case halves require a reamed fit to ensure the case stays in perfect alignment.
Example Sentence 2
During the cylinder overhaul all valve guide holes were brought to a reamed fit before new guides were installed.