Switchcraft MT334BX
3C Mil-jack


Long frame jacks are designed especially for high quality communication equipment, and to meet exacting MIL specifications, as well as telephone and communication systems. Many jacks have WEco equivalent types. MT-Jax® phone jacks are offered in four styles: MT-Jax, WMT-Jax®, XMT-Jax® and YMT-Jax®. Rugged steel frames are produced in specially designed dies, press welded to provide rigidity and dimensional stability required by telephone and communication jack panels - and to meet MIL frame strength tests. "A" and "C" frame styles are available.

TERMINALS: Solder Lug: All MT-Jax have solder lug terminals. Wire-Wrapping Terminals: WMT-Jax have wire-wrapping terminals. Offset Ground Lugs: XMT-Jax and YMT-Jax have ground lugs, which simplify production line wiring time. A single row of jacks can be installed with a single buss wire connected to all ground lugs in a row, or when double rows are mounted on .625 inch vertical centers with lugs oriented between rows, holes in ground lugs line up so a single buss wire provides connections for both rows. XMT-Jax have ground lugs oriented away and YMT-Jax are oriented toward jack frame. See illustration.

MIL STANDARDIZATION: MIL jack types listed have been adjusted for use with plugs specified in Amendment No. 1, MIL-P-642, usually M642/1-1, M642/1-2, M642/2-1, M642/2-2, M642/4-1 or M642/4-2. When applicable, specify the plug you will use; we will adjust with that plug where the item is not a MIL-type. NOTE: MT-Jax jacks Numbers ×MT-342B and ×MT-344B have shorter bushings, 0.5 inches long with a hold inside diameter of .21 inches. They will mate with MIL plug M642/5-1 or M642/8-1. M642/5-1 plug (Switchcraft 480) cannot be used with ×MT-342B or ×MT-344B if these jacks are mounted on standard .625 inch thick panels. The short jack bushings are recessed .125 inch, and the M642/5-1 is too wide to fit in the panel recess. Use plug M642/8-1 (Switchcraft 484) with a narrower diameter to fit in the recess and mate properly.

CONTACTS: Contacts on shuts and isolated switching circuits are welded crossbar palladium. Welded crossbar gold alloy contacts (WEco #1) are available on special order for dry circuit applications.

General Specifications:

  • Frame and Stack Screws: Plated steel, with iridescent iridite finish.
  • Springs: Copper alloy, spring tempered. Solder lugs are tinned.
  • Bushings: Plated copper alloy standard. Natural brass finish optional.
  • Insulation: Rigid plastic spacers (MIL-type PBE-P per Specification LP-513). One piece molded through stack.
  • Contacts: Welded crossbar palladium contacts in shunt and isolated switching circuits are standard. Gold alloy (WEco #1) and fine silver are available on special order.

Mechanical Specifications:

  • Life: Commercial jacks­10,000 insertion/withdrawal cycles, minimum. Military Jacks--20,000 insertion/withdrawal cycles, mimimum.
  • Mechanical Shock: Military Jacks­ Per MIL-STD-202, method 213, Test Condition H (75g).
  • Vibration: Military Jacks­ Per MIL-STD-202, method 213, (10-55 Hz).

Electrical Specifications:

  • Contact Resistance: Commercial Jacks­.030 ohms maximum (initial), .050 ohms maximum (after humidity, durability exposure). Military Jacks­.010 ohms maximum (initial), .020 ohms maximum (after life), .10 ohms maximum (after salt spray).
  • Insulation Resistance: Commercial jacks­10,000 M(omega) minimum (initial), 1,000 M(omega) minimum (after humidity). Military Jacks­10,000 M(omega) minimum (initial), 1,000 M(omega) minimum (after humidity, durability exposure).
  • Dielectric Withstanding Voltage: 500 V, 60 Hz (rms) AC.

Environmental Specifications:

  • Thermal Range: Commercial Jacks­ -55°C to +85°C (non-operating); -20°C to +65°C (operating). Military Jacks­ -55°C to +85°C (non operating); -40°C to +65°C (operating).
  • Thermal Shock: Commercial Jacks­Per MIL-STD-202, method 107. Military Jacks: Per MIL-STD-202, method 107.
  • Humidity: Commercial Jacks­Per MIL-STD-202, method 106. Military Jacks--0% to 95% operating and non-operating.
  • Salt Spray: Commercial Jacks­Per MIL-STD-202, method 101. Military Jacks­Per MIL-STD-202, method 101 (48 hours).
  • Moisture Resistance: Military Jacks­Per MIL-STD-202, method 106 (240 hours).


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