Ooh. I have one.
I was MOCing a while back with some older parts, had one of those black Bohrok head parts and I thought, 'hmm, you know what, I could totally add some Bohrok eyes here and make this thing look way cooler.'
I got one of THESE and a 2-long axle, the kind that didn't have the grooves, mind, and put them into the the side of the part facing the molded on piston.
What a mistake that was.
I went to remove it later and found I couldn't. There was nowhere for me to grab and tug the part back out, or use a brick separator or nails or teeth. It took ages to devise a plan and wiggle the little axle out... by which point, the part the axle had been holding in place had cracked.
So, moral probably should be if I can't find any 3-long axles, I shouldn't try something like that again.