I was really much inspired by Donkey's RSVP Retractable Prototype MX, but i thought he never released tutorial, so i tried to figure out a way...Mine might be different than his.
Tutorial:
Pens you need:
-Uni-Ball Lakubo
-Zebra Hyper Jell
-Pilot Super Grip Knock (Ball point retractable pen)
-Signo Metal Tip
-G2/G-Knock Ink refil
Things You need:
-Safety Pin (0.7mm thinkness if possible)
Tools You need:
-Sandpaper
-Handsaw
-Transparent Tape
Preparation (Told in numbers. That means on assembly, it will be mentioned in these numbers):
1) Take off Lakubo's Grip. Cut the thin barrel (the part where grip used to be), but don't cut completely off the Main Barrel. Leave 4~4.5mm. Sand that 4~4.5mm part until the G2 Refil can fit VERY tightly.
2) Cut the G2/G-Knock ink refil barrel so that the main ink barrel is about 4.6mm. Put a safety pin in middle of the barrel. IMPORTANT: The pin should be little off the center when you look in like in the picture:

Now there's a big hole and a small hole. Put the Pin all the way inside, and cut off both sides. It should look like in the picture. Tape it around so that ur finger wont get hurt.
3) Cut 3~5mm from the back of Lakubo's inktube. Put a tape 1.7cm away from the back.
4) Cut the Super Grip grip's lined part so that it is 1.4cm long.
Assembly:
1) Put the signo tip on the #2 (doesn't really matter which side), and tape it (or use super glue if u want that).
2) Put #2's other side into #1. It should fit tightly becuase you should have sand it tightly. Now tape that or super glue it. It doesn't really matter if u use tape or not because you have to use tape anyway to give thickness to the #2. Do that.
3) Put the Lakubo Grip over #2 and keep it going until it touches the Lakubo Main Barrel. Then tape the front part of Lakubo Grip and then put #4 over the tape.
4) Put #3 through the larger hole of #2, and put the spring on the back of the inktube. It should stop moving because the tape blocks it. Put the insert in.
5) Screw back the Lakubo's back part. and then put Hyper Jell's grip on the thinner section. Then put Hyper Jell's cap on the back. Break off clip of the Hyper Jell's cap and sand it to make it smooth.
6) Finished. To write, put the two side of the safety pin (hard to find cuz hidden by Lakubo Grip) and the inktube would come out because of Spring pressure. To put it back, just push the inkpoint back in on hard surface.
THE END!!!!!!!!! :bowdown: :bowdown: :clap: :clap: :banana: :banana:
Go and spin this thing :spin:
INSERT:

NOTE: Please dont use the PTS insert, cuz ur obviously not in it...i just posted to show it off.