A thru hole, also known as a through hole, is a feature on a blueprint or drawing that identifies a hole to be machined with two open ends. The hole goes all the way through the part. In other words, the hole breaks through at two locations on the part.
In the picture below, the thru hole is on the right. The other holes are blind holes.
How to dimension a thru hole?
A thru hole is dimensioned by specifying the diameter of the hole along with a tolerance. Additional features can be added if needed such as a countersink or counterbore for the hole. No other features are required.
Thru hole vs blind hole
A thru hole has two open ends. A blind hole has one open end and does not go all the way through the part.
Thru hole symbol
There is no GD&T symbol for a thru hole though often it will be specified with the notation “THRU” on the engineering drawing.
Thru hole examples
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