Sorry for lack of detail in first post.

The pen I am looking for is in essence a more durable, refillable version of the uni ball jetstream 101.

I like the pen a lot, as it is also good for maths as well as writing , unlike a fountain pen. However I am annoyed that it is not refillable, and I really just want a pen for life to stop constantly having to buy a new one every 3-4months.