A lot of people that owns an old HP48 might at some point want to transfer programs to them. The original cables are, however, ridicolously expensive.
 

It is, however very easy to make a cable yourself.
All you really do take a 4 pin PH2.0 connector and connect to a serial plug as shown here:
https://www.hpcalc.org/hp48/docs/faq/48faq-12.htm

If you need a little more visual guide, you can find a youtube guide here:
https://www.youtube.com/watch?v=JNTjJ_oEeh8

It is, however pretty annoying to plug and unplug the PH2.0 connector, as it is possible to plug it reversely. 

This model is basically a simple plug to house the PH.2.0 connector in, so that it fits the HP48 perfectly.

If you need a plug for the DB9 serial plug in the other end, I suggest this, which I used:
https://www.thingiverse.com/thing:2104048

Note 1: it is a snug fit and you will have to file all sides of the PH2. 0 a bit to make it fit the connector. 

Note2: recently found out you you can buy a complete usb to PH2. 0 cable so you do not have to solder.