The main advantage of using an O-ring is that it helps to prevent cracking of the pen barrel. When silicone grease is applied to the threads of the pen barrel to prevent ink from leaking, it is easy to use too much force when screwing the pen back together and this can lead to cracks. The O-ring cushions the barrel, but please do not tighten the pen too much or the O-ring can bulge out!
The disadvantages of O-rings are that they usually are sold in packages containing hundreds of O-rings and it can be difficult to choose the right size of O-ring for each different size of pen. Also, an O-ring alone is not enough to safely convert a fountain pen into an eyedropper fill pen.
We have found that silicone grease is essential to convert your pen into an eyedropper pen, and it will work as a good seal even without an O-ring. For over one year now we have been using one eyedropper pen with silicone grease alone and no O-ring and it has worked just fine without leaking.
The trick is that you need to refresh the silicone grease on your pen every time you refill it with ink. Be sure to coat both sets of threads (on the end of barrel and on the main section of the pen) with a generous amount of silicone grease. When tightening the barrel to the pen after you refill it with ink, avoid using too much force so that you will not break the pen. Wipe off any excess silicone grease. This is a simple, cheap method to convert a fountain pen into an eyedropper pen.
One of our favorite fountain pens that can be converted into an eyedropper fill pen is the Kaweco Sport. The threads of this pen are very close together and it has a generous smooth area below the threads to help give it a good seal when used with silicone grease. Additionally, this creates a large ink reservoir so you can write for a much longer period of time than when you use a standard universal fountain pen cartridge. Do you have any experiences with eyedropper fill pens? If so, we’d love to hear from you!
|Without silicone grease, ink seeps past the threads and leaks out of the pen.|
|Using a generous amount of silicone grease on the threads gives a good seal to your eyedropper pen.|
|Don’t use too much force to put your pen back together and then wipe off excess silicone grease.|
|Ink does not seep past the threads or leak from the eyedropper pen sealed with silicone grease.|