A Guide to Mechanical Engineering Terminology

At Nova, we develop products from concept through engineering for manufacturing. Engineering is filled with acronyms and industry jargon that can be intimidating. Add to that a big upfront investment, and it can feel like high stakes. 

Our engineering team is skilled in successfully translating beautiful design into engineered parts that will turn your vision into a reality. Here’s a list of terms you may encounter and what they mean. 

Bearing:

A component that allows smooth rotating or sliding motion. Most common is the ball bearing, in which balls are used between the bearing surfaces to reduce friction.

BOM:

Bill of Materials, a spreadsheet showing each component in the product. Typically shows materials, part numbers, quantities needed, and sometimes price.

Boss:

A protrusion or projection. Often cylindrical but not always, sometimes provides a contact surface around a hole. 

Build:

A set of units that are assembled at any stage of the design process.

Bushing:

Similar to a bearing, but a single component that keeps two other components aligned coaxially.

CAD Database:

Computer Aided Design, software used to design 3D geometry. Often referred to as “CAD files” or just “the CAD”. 

Chamfer (AKA bevel):

A flat surface made by cutting off the edge or corner, or filling in an internal corner.

Cam:

A mechanical device that uses an off-center circle or ellipse on a rotating shaft to create variable or reciprocating motion in another component (cam follower).

Collet:

A cone-shaped sleeve used to hold cylindrical parts, such as a drill bit in a drill. 

Compression set:

A measure of how well a gasket material returns to its original shape after being compressed over a long period of time.

Counterbore:

A hole with a wider cylindrical hole at the opening to keep a screw head flush with a surface.

Countersink:

A hole with a tapered opening to keep a flathead screw flush with a surface.

Coupling:

A device used to connect two shafts together at their ends for the purpose of transmitting power, and to account for slight misalignments.

Detent:

An indentation made to fit another component.

DFM:

Design for manufacturability (alternate term: DPR - Design for Product Realization).

DFMEA:

Design Failure Modes and Effects Analysis. A structured analysis of the ways a product could fail, the impact each failure mode would have, its likelihood and severity, and mitigation plan. 

Die:

Metal plates for forming or cutting a desired shape (eg. hole punch).

DIR:

Design Inputs Requirements. A document detailing the user requirements for the product (eg. the product must be able to be held comfortably for 4 hours) and the corresponding design specifications (eg. the product should be less than 3 pounds). 

DOE:

Design of Experiment. A plan to test a hypothesis to resolve a problem. Commonly used in early builds to find the root cause of manufacturing issues.

DVT:

Design verification test. This build confirms that the product looks the way it is intended to. In this build, molding parameters and colors are tuned to match the CMF spec.

EVT:

Engineering verification test. This build confirms that the product is functioning to the product requirements. In other words, “does it work?”

Fillet (AKA Round):

A rounded surface made by cutting off the edge or corner of an object, or filling in an internal corner. 

Flange: 

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

Float:

Intentional, designed gaps in the assembly to account for a range of tolerances in the parts.

Gage:

A device used to measure a part directly (eg. if the part fits in the gauge, it is not too big to be used in the assembly).

Gasket vs. O-ring:

A component that can be compressed to fill a gap, and is often used for sealing. Gaskets tend to be cut out from a sheet of rubber, whereas o-rings are molded into a complete circle. Though most commonly made from rubber and silicone, gaskets can also be made from cork, felt, paper, and more. 

Jig / Fixture:

Devices used to hold a part in place during assembly or manufacturing.

Kerf:

A channel or groove cut into a material, but not all the way through.

Knurl:

A rough surface added to metal parts to improve grip.

Lug:

Similar to a flange, a projecting part that provides support or allows a part to be attached to another part (often with screws).

MP:

Mass production.

Nominal dimension:

The nominal dimension is the dimension as designed. Eg. Length = 12.0 +/- 0.5mm. 12.0 is the nominal length with a tolerance range of +/- 0.5mm, so parts could range from 11.5 to 12.5mm in length and still be considered “in spec”.

Pinion:

Plain gear, often the smallest gear in a gearset, often the driving gear. May be used with a Gear Rack for linear motion.

Poka Yoke:

Japanese for “mistake-proofing” or “inadvertent error prevention”. These are often mechanical features to ensure parts cannot be assembled backwards.

Prototype build:

This build may be focusing on a particular aspect of the product function. It is generally smaller and performed prior to EVT to inform design decisions. 

PSA:

Pressure sensitive adhesive. This is the type of tape we are most familiar with, from masking tape to packing tape. It is an adhesive that has a strong bond once pressed onto the surface it is bonding to. 

PVT:

Process verification test. This build may be focusing on a particular aspect of the product function.

Ratchet (with pawl):

A gear that only rotates in one direction. A pawl is a spring loaded arm that engages on the ratchet to limit the rotation to one direction.

Relief:

Additional features which have no mechanical function but enable easier manufacturing, eg. an extra groove to facilitate machining a sharp corner.

Rib:

A projecting thin wall which adds strength to a part.

Risk Analysis:

A process for characterizing the level of risk associated with various hazards.

RMP:

Risk management plan. A written plan to mitigate and manage risks.

Shim:

A thin piece of material that can be used to fill a gap.

Shoulder:

A wider part on a cylindrical part (eg a screw head).

Standoff:

A piece of hardware which holds parts at a predetermined distance away from each other.

Stress and Strain:

Stress is the amount of force per unit area a material is experiencing. Strain is the relationship between Stress and how much the material deforms (bends or stretches).

TA:

Tolerance Analysis. A tool to determine how tolerances of various mating parts will stack up in the final assembly, and ensure that the parts can always be assembled. See more from our friends at FiveFlute here

TSA:

Temperature sensitive adhesive (sometimes called HAF: Heat activated film).

Yield Strength:

The amount of stress a particular material can take before it plastically deforms (bends and never returns to the original shape).

Ultimate Strength (Breaking Strength):

The amount of stress at which a material will rupture.

Undercut:

A cut with inward sloping sides, with an overhanging edge. These need to be designed carefully to allow for manufacturability whether machining or molding. 

V&V:

Verification (part meets the spec) and Validation (does it meet users needs through user testing).

You made it! 🎉

This list is actively growing, so be sure to check back for updates. Let us know if there’s a term you think we missed - we’d love to hear from you. As is always true with industry terminology, these are always changing and each manufacturer may have their preferred terms. 

We are rooting for you as you enter into this exciting and challenging phase of product development. Please feel free to reach out to the team at Nova if you need support for your transfer to manufacturing: hello@wearenova.co