The mechanism is a Penn State Industries' TrimlineŠ pen.
Extend the pen point by twisting the pen top clockwise.
Retract the pen point by twisting the pen top counterclockwise.
Replacing the Ink Cartridge
Note the alignment of the two pen barrels. When reassembling the pen, this will allow the pen to be put back in the same arrangement as delivered. (This is not critical to the operation of the pen.) Pull the pen top straight off. (Note that the pen top may be a little stiff until it has been removed and replaced several times.)
Unscrew the refill from the internal tube.
Screw in a new refill (Cross Style Ink Refill). Turn the internal tube counterclockwise to retract the pen point all the way in. Align the barrels as they were before disassembly and push the pen top onto the internal tube until it contacts the metal spacer.
Extend the pen point by twisting the pen top clockwise.
Retract the pen point by twisting the pen top counterclockwise.
Note the alignment of the two pen barrels. When reassembling the pen, this will allow the pen to be put back in the same arrangement as delivered. (This is not critical to the operation of the pen.) Pull the pen top straight off. (Note that the pen top may be a little stiff until it has been removed and replaced several times.)
Unscrew the refill from the internal tube.
Screw in a new refill (Cross Style Ink Refill). Turn the internal tube counterclockwise to retract the pen point all the way in. Align the barrels as they were before disassembly and push the pen top onto the internal tube until it contacts the metal spacer.