What's the difference between the 39-090 and 39-188?

This is a great question! The difference between these two sets of operators is in the shape of the gear arm. You'll notice that each such arm has a kind of "zig zag" design. The precise shape of that zig zag is the definitional difference.

You'll note that the 39-089 and 39-090 have a 'Z' shaped gear arm, whereas the 39-187 and 39-188 gear arm has an extra bend, making more of a 'W' shape. See the images below of the 39-090 and 39-188. 

I know that seems like a subtle change, but it can make a huge difference. 

Let me know if you have other questions!

Dimensions for 39-090

Alternate measurement of arm

Hello there. If you're taking about the detach clip, these come installed with the 39-089 and 39-090, but you can also purchase spares--see the 39-105. If you need new stud brackets, these operators work with many different kinds. See our selection here.