I was tasked by a family member to make one of these for her hummingbird feeder heater.  Couldn't find anything ready to print so I had to design it.  Spent 30 minutes designing it, and it worked first try, so sorry if it isn't the best. 

Uses a 8mm wide by 20mm long spring with and ID of 5ish mm. I just used what I had on hand which was an old spring from my print bed on my ender 3 v2.

The tolerance on the holes for the spring were created so that the spring itself will hold the male piece connected inside the female