After looking at it again, I’m not sure if it even needs a different spring or if this is the default.
That looks like the standard F-701 steel refill. Is it not? It seems you may be right about the different spring, as looking at my G2 refills the steps on the part beyond the barrel of the cartridge and the length does look quite different.
It’s an EasyFlow 9000 Parker style G2 refill with removed end cap.
OK… I was looking at my Pilot G2 gel refills… and that was what I thought you meant when you mentioned G2 refills…
I have a bunch of those and like the gel pens… Thought to try them in a 701
Maybe I will anyway, thought they do look lots different. I can try to take the spring out of a Pilot G2 I guess. Worth a try, if I get a 701 and don’t like the way it writes. Or even get some of the Parker style G2 ones…
I wish I had your self control. I got the TUL gels (on your recommendation) as well as some Paper Mate Profile Gel, Pilot G2, Sharpie S-Gel, Uniball 207, Zebra G750 (black brass), and I got a X701 and put a real Parker G2 gel refill in it. Out of all of them I like the Uniball 207 (IGNO) best for writing feel. It is just so darn smooth and effortless. From there I guess it comes down to feel in the hand, grip, weight… I personally like the design that lets you see the level in the ink refill. Though I think I could live with any of them. There aren’t huge (to me) differences.
Anyway, @raccoon, If you ever run out of your 3 lifetime supply of gel pens, give the Uniball 207 a try.
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For those wanting to test drive some of these.
Office Depot sells most of them in 4 packs.
And no worries about old stock or returned dry ones like some on Amazon report.
Pay more per pen at OD.
My local store has a writing test station where you can test pens.
All the Best,
Jeff
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Good to know. Except for the two Zebras, I bought 2 packs with 2 refills, 4 packs, one six pack, and even one 12 pack (The Uniball 207s before I got crazy on the rest). Whatever got the price per pen to the lowest price (tip, the larger packs are not always the cheapest per pen). The result is I have more pens than I will ever use. I have already given away several. So far, I have not run into any bad (dried out) pens. All of the ones I got were from Amazon. But I do have a concern that by the time I go to use some of them that will be the case.
Thanks for the tip!
The Uniball 207 looks pretty good!
I think I’ll stick to the TUL gels, but if not, maybe I’ll try out those Uniball gels. 
I am sure that you are fine with the TUL pens. Especially with the amount of writing that you have mentioned that you do. The differences between all of the ones I tried is not huge. All of them write just fine, and have much better “feel” than any ball point that I have tried. The Uniball 207 just feels a little smoother and more effortless than the rest. I could easily use any of them and be happy. My OP was more a comment on my lack of control when I start down the road of trying … things! I certainly don’t need all of the close to 30 pens that I have ended up with. Many of them will probably end up being dried out and useless by the time I get around to using them… Time to start giving them away.
I use the Zebra 701 with a Space pen refill, works great. There are videos online about this easy mod.
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I need to check that out. Using the Parker G2 refill works, but it makes it real stiff to actuate …
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I’ve got a Fisher Space Pen bullet in Cerakote black that I’ve had for a little while now and really like it. It’s durable. Writes through almost anything. And it’s small enough to fit in my pocket and not even notice it’s there.
I’ve been using 402s for years, most practical and superb writing pens I’ve come across yet!
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I inherited a 1970s USA made gold plated Cross pen from my great grandfather. It’s very thin, great balance and sturdy feeling, but the weakness is the ballpoint ink. I prefer Uniball Signo for writing.
I’m sad I lost my only Pilot G2. A $1 pen, that would have to be one of my favorites. 