How to identify an unknown connector from a photo or PCB

Measure pitch across many pins, count positions/rows, note mounting and latch features, then filter by those traits against known families; the 2.50 vs 2.54 mm and 1.25 vs 1.27 mm distinctions usually decide it.

What should you measure first?

• Pitch: measure from pin 1 center to pin N center and divide by (N−1). Over 10 pins, 22.86 mm → 2.54 mm; ~22.50 mm → 2.50 mm. Over 20 pins, 25.40 mm → 1.27 mm; ~25.00 mm → 1.25 mm. The cumulative error test (≥0.3–0.4 mm over many pins) is more reliable than single-pin reads. Also record tolerance if you only have photos.

• Positions and rows: single vs dual row; mezzanine arrays; edge/straddle types.

• Mounting: through-hole vs SMT; SMT gullwings vs vertical posts; presence of metal hold‑downs or through‑hole pegs.

• Polarization and locks: friction ramps; side, top, or over-center latches; keyed shrouds; asymmetrical housings.

• Shield/shell: metal shells, threaded bodies, snap rings; board stakes for mechanical load.

Wire‑to‑board pitch reference map

For quick narrowing: 2.54 mm (0.1 in) headers/IDC “box” headers are common in legacy and dev boards; 2.50 mm families (e.g., JST XH) are shrouded and visually denser than 2.54 mm KK‑style posts; 2.00 mm (e.g., JST PH, Hirose DF11) look notably tighter and lower‑profile than 2.5x mm ranges; 1.50 mm (JST ZH) is compact with small shrouds; 1.25 mm (JST GH with a positive side latch; Hirose DF13 with a top boss and friction) is visibly fine‑pitch but still hand‑crimped; 1.00 mm (JST SH) is typically SMT with metal hold‑downs; power families jump to 3.00 mm (Molex Micro‑Fit 3.0), 3.96 mm (JST VH), or 4.20 mm (Molex Mini‑Fit Jr), which look much more massive and have robust latch arms.

Is it board‑to‑board, wire‑to‑board, or FFC?

Board‑to‑board/mezzanine parts show dense pin fields, usually 0.5–1.0 mm pitch, with mated height options and plastic guide posts or alignment bosses. FFC/FPC connectors have flip‑lock or slide actuators, common at 0.3/0.5/1.0 mm pitch; note top‑ vs bottom‑contact and cable entry side (front vs back). Wire‑to‑board parts accept crimped contacts into housings; look for polarization ribs and latch tongues on the receptacle.

What clues are on the PCB and net names?

USB Micro‑B footprints have 5 signal pads in an asymmetrical pattern plus shell stakes; nets labeled VBUS, D+, D−, ID, GND often appear, with a 90 Ω differential pair on D+/D−. USB Type‑C shows 24 SMT pads in mirrored rows with large through‑hole shells; expect 90 Ω pairs (USB2) and ~85 Ω pairs for SuperSpeed lanes and CC1/CC2 nets. RJ45 (8P8C) is near magnetics and 100 Ω differential routing. HDMI has 19 pads and multiple 100 Ω pairs with a shielded cage. microSD sockets show spring contacts in-line plus a card‑detect. RF coax: SMA uses a 1/4‑36 thread and ~8 mm hex; U.FL/IPEX is tiny, snap‑on, ~2 mm mated height; MMCX is push‑snap ~2.4 mm OD.

How do you measure tiny pitch from only a photo?

Use a macro photo with a steel ruler in frame, or scan at 600–1200 dpi. Calibrate pixels/mm from the ruler, then compute pitch as (xN − x1)/(N − 1). Measure across as many pins as visible. If a 10‑pin row is ~22.5 mm center‑to‑center, that’s 2.50 mm; if ~22.86 mm, it’s 2.54 mm. For 1.25 vs 1.27 mm, span 20 pins: ~25.0 vs 25.4 mm.

Common look‑alikes and quick tells

JST XH (2.50) vs Molex KK (2.54): XH headers are more heavily shrouded; KK often shows exposed square posts; over 10 pins, the 0.16 mm accumulated difference is measurable. JST GH (1.25) vs Hirose DF13 (1.25): GH plugs have a clear side latch; DF13 relies on a small top boss with friction. Micro‑Fit 3.0 vs Mini‑Fit Jr (4.2): Mini‑Fit parts are visibly larger with wider housings and heavier latch arms.

Where do you search by features?

Start with distributor filters (pitch, positions, rows, mounting, latch, shroud) on Digi‑Key or Mouser. Cross‑check manufacturer catalogs from JST, Molex, TE, Hirose, Samtec. ECAD libraries (SnapEDA, Ultra Librarian, SamacSys) and Octopart images are useful to visually match latch geometry and polarization keys.

Procurement: which part numbers matter?

Capture the full mating stack: board header/receptacle P/N, mating housing P/N, and crimp terminal P/N, plus plating (tin vs gold) and AWG range. Record row/positions and any locking or keying options. This prevents being trapped by vague “compatible” substitutions.

DFM notes while you confirm the ID

Follow the vendor land pattern and use IPC‑7351 as a cross‑check. Provide solder‑tab fillets and consider paste‑reduction on big shells to limit float. Keep keepouts for latches and cable bend radius; add pegs or reliefs when mating force is high. For high‑speed connectors, route to the target impedances (USB2 90 Ω diff; USB3/PCIe ~85 Ω diff; Ethernet/HDMI 100 Ω diff) and plan return vias for escapes.

What to include when you ask “what connector is this?”

Share a macro photo with a ruler, measured pitch (over many pins), positions/rows, mounting style, latch/polarization notes, and any nearby net names. That’s usually enough to zero in on the exact family.