Types
Since The Doc is struggling to travel, he is doing more research on insulated crimp terminals.

There are 3 broad types of insulated crimp terminals, including:

• Vinyl style, which are often partially insulated;
• Nylon style, which can be fully insulated when they are a blade shape. So, when the male and female parts are mated, all the metal parts are covered with Nylon. Nylon is a premium quality insulation material resistant to petrol, hydraulic fluids and oil; and
• Heatshrink. As the name suggests after you crimp the terminal, you then use a heat gun to heat shrink the insulation onto the terminal and wire. Heatshrink terminals have good dielectric strength (it is a good insulator) and gives a hermetic seal (preventing dust and water ingress). Often used in marine environments or under a car’s bonnet.

The three styles can be plugged into each other, if they are the same size.

Heat shrink terminals are the most expensive to buy, around AUD1.00 each verse AUD36 cents for a vinyl crimp (June 2026).

Tip: do not try and heat shrink a nylon or vinyl covered insulated terminal; they will melt.

Metal type
The better-quality terminals are tin-plated copper. Cheaper terminals, with lower electrical conductivity, are tin-plated brass.

Cheaper terminals are tin-plated brass. Tin-plated copper terminals seem to come in three broad categories; first those sold on eBay, Amazon and Autoparts stores which are often quite thin and more likely to deform when crimped.

Second automotive grade terminals from bigger name companies like NARVA or IONNIC (who sell even better quality terminals than NARVA).

Lastly, military grade terminals which are expensive to buy, but are of a very high quality. These terminals have more copper and a thicker tin plating.

Features
Besides being made of tin-plated copper, better quality crimps can also have some or all of these features:

• terminal sizing is stamped onto the terminal. Two sizes can be stamped, the wire gauge in AWG (or metric) and the terminal sizing (e.g. the size of the ring terminal opening). All the IONNIC terminals I have seen were stamped and most of the NARVA terminals too;
• a bell housing/bell mouth where the wire is inserted. The bell mouth helps accommodate the fine wire strands, which can splay out after stripping. The bell mouth makes wire insertion easier. Sometimes the bell mouth is formed by the insulation, with others it is part of the metal terminal, like IONNIC Double Crimped terminals;
• in the middle of butt splice terminals, the terminal has been pressed to stop the wire going past the halfway point, as these butt splices are crimped on both sides to join the two wires;
• on NARVA terminals, but not IONNIC, there is a stop point pressed into the terminal preventing you from inserting the wire too far before crimping (The Doc means terminals other than butt splices). Good practice is to allow 1 to 2mm of copper wire to protrude through the terminal before crimping;
• with heatshrink terminals the insulation is longer, so when heat is applied, the heatshrink covers part of the wire to secure a waterproof connection. With nylon and vinyl style terminals you can use a single wall heatshrink tubing it needed. The Doc chooses to use only single wall tubing on nylon and vinyl style terminals, but you could use a dual wall tubing; and
• occasionally a terminal will have an additional tin-plated copper sleeve at the wire insertion end, called a double crimp. INONIC terminals made like this are labelled “Double Crimp”.

Terminal sizes
Automotive terminals commonly come in three sizes red (AWG22-16 or 0.5-1.5mm2), blue (AWG16-14 or 1.5-2.5mm2) and yellow (AWG12-10 or 2.5-6mm2). Or small (red), medium (blue) and large (yellow). AWG stands for American Wire Gauge and the second figure is the metric sizing.

A better-quality terminal means a better crimp, less resistance, less heat and better conductivity.

The Doc’s Guide to terminal crimping is here.