How to identify a connector
Start with where it came from: the same 2-pin plug means different things on a LiPo cell, a PC fan or an LED strip. Then measure the pitch, the distance between the centres of two neighbouring pins, and count the contacts. A latch you have to press, and whether it joins two cables or plugs into a board, settle most of the doubts that remain.
Measure the pitch
A caliper is enough, as long as you measure across the whole row: from the centre of the first pin to the centre of the last, divided by the number of pins minus one. On a 6-pin connector the span is 5 pitches, so 10 mm means 2.0 mm and 12.5 mm means 2.5 mm. Two pitches cause most mix-ups: 2.5 mm (JST XH and SM) and 2.54 mm, the tenth of an inch of Dupont and Molex KK.
| Pitch | Connectors |
|---|---|
| 1.0 mm | JST SH |
| 1.25 mm | JST GH, Molex PicoBlade, Hirose DF13 |
| 1.5 mm | JST ZH |
| 2.0 mm | JST PH, Grove |
| 2.5 mm | JST XH, JST SM, JST RCY |
| 2.54 mm | Molex KK 254, Dupont, servo plug |
| 3.0 mm | Molex Micro-Fit 3.0 |
| 3.96 mm | JST VH |
| 4.2 mm | Molex Mini-Fit Jr |
Pitch from the makers’ catalogues. Power plugs (XT, Deans, Anderson) and barrel plugs are recognised by their shape, not by pitch.
Every connector in the identifier
| Connector | Pitch | Per contact | Latch | Mating |
|---|---|---|---|---|
| JST SH | 1.0 mm | 1 A | no, held by friction | wire-to-board |
| JST GH | 1.25 mm | 1 A | yes, a tab to press | wire-to-board |
| Molex PicoBlade | 1.25 mm | 1 A | no, held by friction | wire-to-board and wire-to-wire |
| Hirose DF13 | 1.25 mm | 1 A | no, held by friction | wire-to-board |
| JST ZH | 1.5 mm | 1 A | no, held by friction | wire-to-board |
| JST PH | 2.0 mm | 2 A | no, held by friction | wire-to-board |
| Grove | 2.0 mm | — | yes, a tab to press | wire-to-board |
| JST XH | 2.5 mm | 3 A | no, held by friction | wire-to-board and wire-to-wire |
| JST SM | 2.5 mm | 3 A | yes, a tab to press | wire-to-wire |
| JST RCY | 2.5 mm | 3 A | depends on the version | wire-to-wire |
| Molex KK 254 | 2.54 mm | 4 A | no, held by friction | wire-to-board |
| Dupont | 2.54 mm | 3 A | depends on the version | wire-to-board and wire-to-wire |
| Servo plug | 2.54 mm | — | no, held by friction | wire-to-board and wire-to-wire |
| Molex Micro-Fit 3.0 | 3.0 mm | 8.5 A | yes, a tab to press | wire-to-board and wire-to-wire |
| JST VH | 3.96 mm | 10 A | yes, a tab to press | wire-to-board |
| Molex Mini-Fit Jr | 4.2 mm | 9 A | yes, a tab to press | wire-to-board and wire-to-wire |
| XT30 | — | 15–20 A | no, held by friction | wire-to-board and wire-to-wire |
| XT60 | — | 30–35 A | no, held by friction | wire-to-board and wire-to-wire |
| XT90 | — | 45 A | no, held by friction | wire-to-board and wire-to-wire |
| Deans (T-plug) | — | — | no, held by friction | wire-to-wire |
| Anderson Powerpole | — | 15–45 A | no, held by friction | wire-to-wire |
| DC barrel plug | — | 2.5–3.5 A | no, held by friction | wire-to-board and wire-to-wire |
Current is the maximum per contact at the wire size the maker states, from the datasheets linked on each connector’s page.
Crimping, current and polarity
Crimp terminals are made for one range of wire sizes and one crimper die. Pliers crush the terminal instead of rolling its wings round the wire, and the contact works loose: ready-made leads are often the easier way. Housings and terminals of different series don’t mix, even at the same pitch.
A rating such as 2 A per contact holds for the wire size the maker tested; with thinner wire or every contact loaded, stay well below it. The connector alone never guarantees polarity either: LiPo plugs, barrel plugs and LED strip leads all exist with both wirings, so check with a multimeter before you plug in something you didn’t wire yourself.
DC wire size and voltage drop calculator →
Frequently asked questions
What is a JST connector?
JST is a Japanese maker, not one connector. On a shop listing, “JST” usually means a JST PH (2.0 mm, small LiPo cells), a JST XH (2.5 mm, balance leads), a JST SH (1.0 mm, Qwiic) or a JST SM (LED strips): measure the pitch to know which.
How do I measure the pitch of a connector?
Measure from the centre of the first pin to the centre of the last and divide by the number of pins minus one. Over many pins the small differences add up: ten pins at 2.5 mm span 22.5 mm, at 2.54 mm they span 22.86 mm.
What connector do Qwiic and STEMMA QT use?
A 4-pin JST SH, 1.0 mm pitch, with GND, 3.3 V, SDA and SCL in that order. The older STEMMA, without QT, uses 3- and 4-pin JST PH at 2.0 mm.
Is a Grove connector the same as a JST PH?
No. Both have a 2.0 mm pitch and Grove has 4 pins, but the Grove housing has a latch and the two don’t mate. Use an adapter cable.
Which polarity is right for a LiPo battery plug?
There is no standard for the 2-pin JST PH on small LiPo cells: Adafruit and SparkFun boards expect one order, some other brands use the reverse. Check with a multimeter. The simplest fix is a reversing adapter; if you swap the two terminals in the housing instead, lift the tab with a needle and move one terminal at a time, and cover the loose one with insulating tape: on a charged cell, two bare terminals touching are a short circuit.
What is the difference between XT30, XT60 and XT90?
Size and current. The number is roughly the brief peak current; Amass rates them about 15–20 A, 30–35 A and 45 A continuous, with 16–18, 12 and 10 AWG wire.
How can I tell a 5.5 × 2.1 from a 5.5 × 2.5 barrel plug?
Only the hole differs. A 5.5 × 2.1 plug won’t go onto the 2.5 mm pin of a 5.5 × 2.5 jack; a 5.5 × 2.5 plug goes onto a 2.0 mm pin but wobbles and can lose contact. A 2 mm drill bit makes a quick gauge.