Linear actuator using geared retract motor.

I designed parts to make an actuator from these geared retract motor units I have.

This is the motor unit I used:
http://www.ebay.com/itm/Worm-Motor-Control-Board-for-Retractable-Electric-Landing-Gear-/172104935631

EDIT:
After playing with it for a while I noticed that they will reverse if they are blocked or if the channel is flipped when they are unpowered. I bought my motor units six months ago, so this issue may be fixed now, but for now I can't recommend buying these motors unless they are confirmed fixed.

Assembly:
1 - Thread the plunger onto the M3 shaft half way down. A nut can be slid into the slot on the underside of the plunger for a stronger thread.
2 - Insert the plunger end and the switch board into the housing.
3 - Carefully slide the board and motor unit into the housing. The board should be pushed in by the edge of the gearbox, and the gearbox should be oriented with the protruding small gear pointing up towards the board/empty space so that it doesn't r