Waterproof Circular Connectors: GX, SP Series — China Sourcing Reference

GX-series and SP-series circular connectors are the dominant connector format for field-deployed electronics outside of formal industrial automation — outdoor sensors, LED lighting systems, industrial IoT nodes, underwater equipment, portable instruments, and custom machine builds. They are colloquially called “aviation connectors” in Chinese supplier catalogs (航空插头), a legacy name with no relationship to actual aerospace standards. GX16 is the single most counterfeited circular connector type produced in China: the market contains a large volume of physically identical but materially inferior units that fail at thread engagement, O-ring sealing, or contact reliability within months of deployment. Incoming inspection and first-article testing are essential when sourcing GX connectors for IoT modules and field-deployed sensor nodes.

Overview

GX-series connectors (GX12, GX16, GX20) use a screw-lock thread mechanism and are available in panel-mount and cable-end configurations. SP-series connectors (SP13, SP17, SP21) are dimensionally similar to Lemo Series B but are non-keyed and significantly cheaper. Neither series has a governing IEC standard — they are market-standard connector families defined by Chinese manufacturers and widely copied. IP67 is claimed by most manufacturers; IP68 is available from a subset. The absence of a normative standard means mechanical and electrical performance varies substantially between manufacturers even for physically identical-looking products.

Key Specifications

GX Series

Contact material (standard): copper alloy, tin-plated. Gold-plated contacts available as option — specify when ordering for low-level signal applications. Working voltage: 250V AC (GX12/GX16), 500V AC (GX20 power variants). Shell finish: nickel-plated aluminum or silver-plated brass — specify brass for higher conductivity shell grounding in shielded cable applications.

SP Series

SP connectors use a push-pull or screw-lock locking mechanism depending on variant. They are physically similar in appearance to Lemo Series B connectors but are not keyed, not mechanically interchangeable, and do not meet Lemo’s IP68 specification. Do not substitute SP series for Lemo connectors in medical or broadcast applications where Lemo IP/keying requirements are specified.

Main Variants

GX16: Thread-Lock vs. Push-Pull

Standard GX16 uses a screw-lock thread (M16 × 1). The panel-mount female (receptacle) has a threaded ring; the cable-end male (plug) screws onto it. Engagement requires approximately 3–5 full turns. Push-pull GX16 variants exist but are less common and not cross-compatible with standard screw-lock panels.

Male/Female Convention

The industry convention for circular field connectors is:

• Panel-mount = female receptacle (receives male contacts, flush with panel surface, exposed when disconnected)
• Cable-end = male plug (exposes male pins, connects to panel receptacle)

This convention matters for ordering — “GX16 4-pin male” is the cable plug; “GX16 4-pin female” is the panel socket. Some Chinese suppliers use non-standard terminology (“male” referring to the shell thread direction rather than the contact type). Verify by requesting photos or mechanical drawings showing pin vs. socket contacts before placing a volume order.

Panel Mount vs. Cable Mount

Panel-mount receptacles install through a 16mm hole (GX16), 12mm hole (GX12), or 20mm hole (GX20) with a locknut. Panel cutout must be clean and deburr-free — a rough edge cuts the O-ring on the panel-mount flange, compromising the IP seal between the connector and panel. Cable-end plugs terminate by crimp or solder at the wire contacts, with a strain-relief boot over the cable exit.

GX20 for Higher Current

GX20 rated at 10A per contact handles loads that GX16 cannot — 24V DC at 10A, motor brake circuits, actuator power. It is less commonly stocked in Chinese distributor catalogs than GX16; lead times from Weipu and Cnlinko are typically 1–2 weeks.

Sourcing from China: What to Look For

The GX16 clone problem is pervasive. A genuine GX16 connector from Weipu (威浦) or Cnlinko has: M16 × 1 threads with 60-turn engagement capacity before thread wear, silicone O-ring at the mating face (compressible at −40°C, UV-stable to 150°C), brass contacts with ≥ 0.5 µm gold or ≥ 3 µm silver plating, and a die-cast aluminum shell with surface hardness adequate to resist thread galling. Clone GX16 units (which represent the majority of Alibaba listings below ¥3/unit) have: zinc alloy or low-grade aluminum shells that gall at 15–20 thread engagement cycles, PVC or NBR O-rings that harden below −10°C and degrade in UV within 6 months, and contacts plated with < 0.1 µm gold flash or bare copper.

Specify materials explicitly in the purchase order. A purchase order that states “GX16 4-pin IP67” will receive the cheapest available unit. Add: “silicone O-ring, brass contacts, gold-plated ≥ 0.2 µm, aluminum alloy shell, nickel-plated.” This filters out the lowest-quality clone products and gives you grounds to reject non-conforming deliveries.

Thread engagement test. Request that incoming inspection includes a thread engagement count: mate and unmate 30 times, inspect thread engagement quality under 10× magnification, and measure unmating force. Genuine connectors maintain smooth engagement; clone connectors show visible thread wear or galling within 20 cycles.

O-ring material verification. Silicone vs. PVC O-rings are not distinguishable by visual inspection. For high-volume sourcing, send samples to a lab for FTIR analysis ($80–150 per sample). For small orders, a simple test: expose the O-ring to 80°C for 24 hours — silicone retains elasticity, PVC hardens and may crack.

Manufacturer options. Weipu (威浦, Wenzhou) is the reference manufacturer for GX and SP series; their products are available through RS Components, Mouser (limited lines), and directly. Cnlinko (中联科华, Shenzhen) is a legitimate second-tier manufacturer with stronger focus on push-pull and IP68 variants for outdoor LED and IoT applications. Holin (深圳浩联) and Xuanwu (玄武) are smaller manufacturers producing GX-series at lower price points; quality documentation is limited but they do supply identifiable production lots with traceable batch numbers. Avoid anonymous “aviation connector” listings with no manufacturer identification — there is no basis for incoming inspection or quality escalation.

IP68 claims. Most GX16 units claim IP67 (1m, 30 minutes per IEC 60529). IP68 claims for GX connectors should specify depth and time — ask for the test report. Legitimate IP68 GX connectors exist (Cnlinko has tested units at 3m / 24h) but they represent a minority of the market. A cable-end GX16 submerged without verification of IP68 will flood at depths below 1m.

Common Issues

O-ring not seated on panel-mount installation. The panel-mount receptacle has an O-ring at the panel interface (between flange and panel surface) that is separate from the mating-face O-ring. This panel O-ring is loose and can be displaced during installation. If not seated in the groove before the locknut is tightened, the panel seal fails while the mating seal remains intact — the connector appears to seal at the front but water ingresses through the panel cutout. Specify in assembly instructions that the panel O-ring must be visually confirmed in-groove before locknut tightening.

Contact solder cup fractures from thermal cycling. Many GX16 cable-end plugs use solder-cup contact termination. If the solder joint is not fully filled (cold joint) or the wire is too large for the cup, the joint fractures under repeated thermal cycling (−20°C to +60°C outdoor). Specify crimp termination for connections subject to thermal cycling, or require a solder joint pull test (≥ 20 N per wire) during incoming inspection.

Incorrect pin count for cable OD. GX16 connectors with high pin counts (8–10 pin) have small contact spacing, limiting the wire gauge to 22–24 AWG. Standard sensor cable (20 AWG, 6mm OD) may not fit through the strain relief of a 10-pin GX16. Match pin count to wire gauge and cable OD — request the strain relief cable range from the manufacturer’s datasheet before finalizing the connector selection.

Shell contact between male and female halves. GX connectors make metal shell-to-shell contact on mating. If the shell is used as a shield or ground path, this is useful. If the cable shield is floating, the shell contact creates an unintended ground loop. In instrumentation applications with signal grounds, specify isolated mounting hardware or verify shell grounding against the system’s EMC design.

Related Resources

• M12 Industrial Connectors — M12 is the standardized alternative for industrial Ethernet and sensor connections where IEC compliance is required
• M8 & M16/M23 Circular Connectors — IEC-standardized circular connectors for servo and sensor applications
• RoHS Compliance — relevant for contact plating material (lead-free solder, restricted substances in plating)
• CE Marking — LVD and EMC compliance for equipment using GX/SP connectors in EU markets
• ESD Protection — GX connectors on field-deployed IoT nodes require ESD coordination at the enclosure interface
• Factory Audit Checklist — audit scope for connector manufacturers, including O-ring material and plating verification
• Electronics Quality Inspection
• Industrial IoT & IIoT Sourcing
• IoT Modules & Components Sourcing