Text copied from TM 5-280, 1963 :

The SF3 consists of a bakelite case about 7,62 centimeters high and 7,9 centimeters in diameter with a screw-on lid containing a built-in fuze case, a spring-loaded striker with a release disk held down by a flat metal safety-and-arming bar, a striker-retaining arm, a glass vial of chemical, a soluble pellet, and an arming spindle that when turned crushes the vial of chemical.

An arming cord was attached to the safety and arming bar. The fuze is covered by a rubber waterproofing cap.
The 7-ounce main charge, integral with the device, is cylindrical and hollow like a section of pipe.
**more text scroll down**

Photos © Joachim.

Scans and info thanks to K. Kamperman.

a- Use :

This antilift is used to activate mines and as a boobytrap.

b- Functioning :

When the retaining weight is lifted, the striker release disk rides upward under the force of the compressed release spring until the top of the striker retaining arm is no longer held in place by the projection on the under side of the striker release disk.
The spring-loaded striker then forces the bottom of the striker retaining arm to tilt outward, releasing the striker against the percussion cap.

c- Installing and Arming :

(1) Before laying, loosen the arming cord from the lid to which it is fastened.
(2) Lay the device on a firm base in a deepened mine hole with the safety-and-arming bar pointing to the right, when facing the enemy, and with the arming cord lying out to the rear.
(3) Carefully press the earth around the device, keeping the top clear and the safety-and-arming bar free to move.
(4) Place the mine to be activated centrally on top of the device.
(5) Fill the hole.
(6) Pull lightly on the arming cord, rotating the safety-and-arming bar 90degrees. This causes the arming spindle to crush the glass vial of chemical, which dissolves the safety pellet and thus arms the mine.

d- Disarming procedure :

Once armed, this device cannot be disarmed. Destroy the device and mine in place.