Hi Justin, thank you for posting,
Your handle resembles the 39-226 with a 5/16" hex. However replacing the handle alone may not fix the issue. When these handles fall out, its usually because the collar in the operator hole has stripped. The handle may actually be in good working condition; in most cases, its the operator that is broken.
The bad news is that the collar cannot be repaired or tightened. There are two options for you to consider.
The first option would be to replace the full operator along with a new handle. Start by taking a look and reviewing the style of the 39-399 operator with the 39-232 handle to see how it compares to your original. This is a newer modern version, so a new handle will be necessary.
The second option is to use glue or even scotch tape on the handle stem to pad it out and help it "bite" into the operator hole. This is only a temporary solution that may only give you a few extra years of usage, if you are not interested in replacing the full setup at this time.
Please review and let me know if you have any additional questions.
