1) All of the pens will take the Parker G2 refill.
G2 is what they call it and it refers to the size, NOT to be confused with the Pilot G2 which will NOT fit.
2)Parker-Type G2 Refills
The 'Parker-style' ballpoint refill is actually a standard pattern refill known as the G2, and is used by many manufacturers for their ball pens. The Parker refill is simply the best-known and most widely available. The G2 refill is 98mm long and approximately 5.8mm diameter on the main barrel. They are easily recognized by the distinctive shape and the sculpted plastic end which is used by some pen retractor mechanisms.
Note: Not to disparage the Parker refills but I have found the GEL to have problems with leakage between the rear plastic cap and the metal barrel.
When this happens the sealant for the ink contaminates the inside of the pen with a sticky honey type material which will accumulate dirt and slow the action of the pen down.
If this happens you can simply clean the inside of the top barrel with isopropyl alcohol or hot soap and water making sure it is dry before putting back together.
For this reason I do not recommend the Parker GEL and I no longer supply it in my pens.
3) Fisher Space Pen refills will fit as long as you put the plastic adapter that comes with the refill over the end of it.
Note: A few of the medium refills have had small burrs on their tips at the junction of the solid tip and the metal barrel. If you find one of these you can remove it with a fine file or sandpaper.
4) Lubrication should never be used on the pen mechanism for I designed them to be maintenance and trouble free. Using lubrication will only attract dust and slow down the action.
The Itoya GPR-7BKBP is currently being used.
It is also called the Itoya Aqua Roller Gel Refill and has a SKU number of 075633302296.
5) To prevent losing the return spring when changing the refill please do this:
Unscrew the bottom barrel but before taking it off put your thumb and index finger over the top of the bottom barrel and then pull the refill out. Your fingers will keep the spring inside of the bottom barrel and you will never lose it. If you have to remove it for some reason put it in a safe place where it cannot roll away and get lost.
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