Some mechanical terms worth knowing

Ball and Detent :
 A simple mechanical arrangement used to hold a moving part in a
temporarily fixed position relative to another part. The ball slides within a bored cylinder, against the
pressure of a spring, which pushes the ball against the detent, a hole of smaller diameter than the ball.
When the hole is in line with the cylinder, the ball falls partially into the hole under spring pressure,
holding the parts at that position. Additional force will push the ball back into its cylinder, compressing
the spring, and allowing the parts to move.
Bearing :
 The part of a machine within which a rotating or sliding
shaft is held. In some bearing types, balls or rollers are used between the bearing surfaces to reduce
rolling friction.

Bell crank:

 A pivoting double lever used to change the direction of applied motion. 

Boss : A cylindrical projection, as on a casting or a forging. Usually provides a contact surface 

around a hole. 

Broach:

To finish the inside of a hole to a shape other than round, as in a keyway (n) The tool for the 

process, which has serrated edges and is pushed or pulled through the hole to produce the required 

shape. 

Clevis :

A U-shaped piece with holes into which a link is inserted and through which a pin or bolt is 

run. It is used as a fastening device which allows rotational motion. 

Collar :

 A cylindrical feature on a part fitted on a shaft used to prevent sliding (axial) movement. 

Core:

 To form the hollow part of a casting, using a solid form placed in the mold (n) The 

solid form used in the coring process, often made of wood, sand, or metal. 

Counterbore:

 A cylindrical flat-bottomed hole, which enlarges the diameter of an existing pilot 

hole. The process used to create that feature.

Countersink  A conical depression added to an existing hole to accommodate and the conic head 

of a fastener recessing it below the surface of a face. The process used to create that feature.

Coupling :

 A device used to connect two shafts together at their ends for the purpose of 

transmitting power. May be used to account for minor misalignment or for mitigating shock loads. 

Die :

 One of a pair of hardened metal plates or impressing or forming desired shape. Also, a tool 

for cutting external threads. 

Face : 

 To machine a flat surface perpendicular to the axis of rotation of a piece.

Fillet :

 A rounded surface filling the internal angle between two intersection surfaces. Also Rounds

Fit :

 The class of contact between two machined surfaces, based upon their respective specified 

size tolerances (clearance, transitional, interference) 

Fixture :

A device used to hold a workpiece while manufacturing operations are performed upon 

that workpiece. 

Flange:

 A projecting rim or edge for fastening, stiffening or positioning. 

 Gage :

 A device used for determining the accuracy of specified manufactured parts by direct 

comparison..

Gage blocks :

 Precision machined steel blocks having two flat, parallel surfaces 

whose separation distance is fabricated to a guaranteed accuracy of a few millionths of an inch; 

Spotface :

 a round machine surface around a hole on a casting or forging, usually to provide a 

contact surface for a fastener or other mating component, the process used to create that feature 

Shim : 

A thin strip of metal inserted between two surfaces to adjust for fit. The process 

of inserting shims. 

Sheave :

 A grooved wheel used to accommodate a belt for the transmission of power. 

Sometimes referred to as a pulley sheave. 

Retaining Ring:

 A tool steel ring used in conjunction with a shaft groove or internal groove to 

located or control position of a component. 

Planetary Gears:

 A gearset characterized by one or more planet gear rotating 

around a sun gear. Epicyclic gearing systems include an outer ring gear (known as an annulas) with the 

planetary system.