I created this key cap for a small project I'm working on that uses four Cherry MX switches in a row (4 key 555 timer piano). The other typewriter keys available fit great but were a bit more difficult to print. I added a fillet to the base of they key in order to create a stronger part, and to provide some support to the part as the smaller details are formed.
Print with a cool hotend temperature. A high temperature hotend will cause the cross part to ooze and over extrude; this will ruin the fit.
On my particular Wanhao Duplicator i3 V2 (Monoprice Maker Select V2) with Hatchbox PLA I am running temps between 200 and 208 for this part. 205 seems to give good layer adhesion and minimal oozing. Your printer may be different, but print it as cool as you can without getting layer adhesion issues.