Definitions of Technical Terms
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Terminal Lug Definition
Terminal Lug. A device attached to a conductor to permit connection to a terminal. A terminal designed to be affixed, usually at one end, to a post, stud, chassis, or the like for mounting. It has provisions for attachment of wires or similar electrical conductors in order to establish an electrical connection and could require the use of tools for attachment of wire.
A terminal may be attached to a wire by a number of methods including screw-on, press-on or crimp-on [which is shown below]. Selection is based on two main criteria ; the wire size the barrel is designed to accept [AWG], and the tongue with will fit a particular stud size. The barrel may be insulated [Type 2] or non-insulated [Type 1]. Normally both insulated or non-insulated should have the wire crimped on, but in some cases the non-insulated lugs may be soldered.
There are a number of styles including three and four way. The eyelet may be Ring, Block Spade, Spring Spade, Flanged Spade, or Hook. Some terminal lugs also have two eyelets.

The diagram above shows a preinsulated Terminal Lug.

This diagram shows a Terminal Lug attached to a Terminal Stud.
There are four main types of terminal lugs;
Basic Terminal with insulated nylon
support sleeve. Basic terminal with permanently attached
insulating sleeve. Basic terminal bonded with silver brazing
alloy. Basic terminal with butted seam.

Terminal Lug Assembly
Standard Gauge Terminals;
22-18 Gauge. 16-14 Gauge. 12-10 Gauge. 8 Gauge. 6 Gauge. 4 Gauge. 2 Gauge. 1/0 - 4/0 Gauge.
Standard Stud Sizes
1/4, 5/16, 3/8, 7/16, 1/2, 3/4
MIL-T-7928G
Terminals, Lug: Splices, Conductor: Crimp Style, Copper, General Specification for (S/S BY SAE-AS7928)
Related topics on Terminals;
Terminal Block Vendors
Definition of Terminal Block / Terminal Board
Lug Implementation Note: The number of wires terminated in an individual terminal or lug should not be greater than three. Multi-section turret, bifurcated, or multi-hole lug terminals should have not more than three wires per section, tong, or hole. In no case should the total cross sectional area of the terminated wires exceed the cross sectional area capacity of the terminal or lug.