My Ranga ebonite dip pen won't fit into the holder with zebra g nib.
Is there a video on YouTube that shows how it's done?
What size is the feed (diameter of the rounded end on the back)?
The zebra nib fits, if this is 5mm. You can remove the feed and place the nib on top of it and see if they match. If there is a small gap, you can heat set the feed to match the profile of the nib.
If you are only going to use this with a G nib, you can also use a file to adjust the size of the hole in the holder. Being ebonite, it's fairly easy to file off a little material. This can be done if the feed is the 4mm feed.
If the feed is larger, you will need to get a No 5 feed and use a little tape on the bottom to press fit it into the holder.
I don't think there is a Youtube video for this.