I have a DFrobot LCD shield that has flat plunger type momentary switches. E.g:
I was planning on putting it inside an enclosure and wanted a way to have buttons on the outside (aka button caps) like
obviously those don't work with the circular button top.
Any ideas or experience?
Normally this kind of push button is used with a captive buttons on the front panel that just rest against the switches - this allows a certain misalignment between PCB and panel without it showing. Such panels are purpose designed and not off the shelf, typically. A 3D printer could help for this(!)
You need a switch cap with a rim/ring to prevent the cap fallout out of the enclosure - but it might be hard to get one the exact size and spacing you need.
Something like this
http://www.rapidonline.com/Electronic-Components/Buttons-for-12-x-12mm-tactile-switches-71594
or
http://www.rapidonline.com/Electronic-Components/1D-Series-caps-for-tactile-switches-80567
Just sits on top of the switch, if you need to extend it (as I have in the past) you just need a bit of plastic tube (or wood, or anything the right size and shape) - to glue to the underside of the cap to give you the extension you need.
The glued on extender has an advantage too, you can file it down once you screw the case on and discover that one of the switches is permanently held down because you screwed it a bit too tight.