I've done this one! You need a couple of things - I took a pen with me to the hardware store to make sure everything fit. First, you need a piece of small rod stock - I think I used 1/8 in. Separate the 2 halves of your pen, find a size rod that will slide down through the center of the transmission till it bottoms out in the tip of the pen (You want the largest diameter rod that won't bind in the transmission). When disassembling, I just hold the pen in my hand, slide the rod through the xmission, then whack it with the hammer till the tip comes out. Now you need a bolt that will fit closely into the tube without binding (1/4" for a 7mm pen, get about a 3" bolt). After removing the tip, put the bolt into the end the tip was in and tap out the transmission. If you don't have the hand strength to hold the pen while you tap it, you can set the transmission end over a drilled waste blank (without a tube)and tap till the xmission falls through. Hope that makes sense.