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UMNOP-1 is a versatile booby trap fuze for use with mines and demolition charges.
The tubular metal body houses a spring-loaded striker which can be retained directly by a radial safety pin (which runs through the fuze body and striker), or by either arm of a C-shaped sear.

The top arm of this sear is bevelled and the bottom arm cut square. The sear is attached to a hinged lever which is normally held in place against the fuze body by an axial pin.
Beneath the lever are two hinged legs, made from split pins, which keep the fuze upright when set in the pressure or pressure release modes. Nails can also be driven through the loops in the legs to fix the fuze into position.
A stab-sensitive detonator assembly is bonded into the fuze body, which has a male M10 × 1 thread and sealing O-ring. The radial pin, normally used for safety, is secured with thin lockwire.
The body of UMNOP-1 is normally unpainted, with its designation stencilled in black.

Once positioned in the charge or mine, the fuze can be set up in any of the following modes:
Pressure :With the axial pin removed, the lever can be pivoted up to an angle of approximately 30°. In this position the lower (squared) arm of the sear engages the striker, allowing safe removal of the radial pin to arm the fuze.
When the lever is then forced down, the lower arm of the sear releases the striker onto the detonator assembly.

Anti-lift : To set for pressure release, a load exceeding 4 kg is placed on the lever and both pins extracted. The top arm of the sear retains the striker until the load is removed and the lever is allowed to rise.
Axial Pull : The fuze set up for axial tripwire pull by extracting the radial pin and ensuring that the lever is free to move. When the axial pin is pulled, the striker bears on the bevelled top arm of the sear. As the sear is pushed away, the lever rises and the striker is released.
Radial Pull : With the lever free to move, the axial pin is removed to arm the mine for radial pull. The striker is then retained only by the radial pin, which can be attached to a tripwire. When this pin is extracted, the striker pulls free from the sear as the lever flips up.

Photos © Josip.

Photo on the right and below © Allan "spotter" Brown.
This is the UMNOP-1V.

Box of UMNOP-1V

Shown on the right and below is a full box of the UMNOP-1V, which is the training version of the UMNOP-1.
Hence the yellow diagonal stripe on the box, this also indicates that the contents is for training purposes.

Photos © M. Jochoms