It's called the Needle Beetle II needle selector. 
The Needle Beetle needle selector selects needles and pushes them in to
"E" position so that you can then perform Tuck, Slip, Lace, Fairisle, etc. 
You hand-select the first 8 needles in to the arrangement you want, then 
push the Needle Beetle II across the needle bed and it will select the rest 
of the needles lickety-spilt! Yes, this is similar to the old KA-7668 (no longer being made)  
 but with one major difference, the old KA-7668 selected the needles only to "D" 
position - you had to then push them manually to "E" position.  
The Needle Beetle II will work on:
All the Brother KX plastic knitting machines KX-350. 355, 360, 
and all the Brother Convertible machines  KX-390, KX-395, KH-400.

(*if you're looking for the original Needle Beetle to fit your Silver Reed/Studio/Singer 
plastic machines: LK-150/140/100, GK-370, and Zippy 90, go to the kriskrafter website
or check my other listings.)

You will need to select which machine you are ordering for, then your Needle Beetle will be 
set for that machine.  

There are several demo videos on Youtube, here are a couple, 
check them out to see how it works! 
https://www.youtube.com/watch?v=5LuupKUF5UA&t=10s
https://www.youtube.com/watch?v=6fhGjwm2wqk&t=330s

I always try to ship within 24 hours.  

Thanks for looking!