This might be the smallest model you'll ever successfully print.  Bold claim, I know.  But if you need this model, then you understand why it is designed the way it is.

I had the connector on a ceiling fan speed pull chain break and the rest of the chain disappeared into the light on the ceiling fan.  This one simple disk of material, no larger than .400" diameter (10 mm), would have saved me from all the time and risk of disassembing the irreplaceable glass globe on the ceiling fan (there's no way the ceiling fan manufacturer has a new one for me to go buy if I break this one!).

The stopper/retainer is designed for .120"/3 mm pull chain with .150"/3.8 mm pitch between balls.  It snaps in place.  It's so small I printed it in white and you can't even see it on the fan.