Lower knife #X75233-0-01 

Fits Brother Overlocker/Serger models:
730, 730D, 730DE, 760D, 760DE, 925D, 935D

and Bernina overlocker/serger mod. 800;

also Husqvarna Viking overlocker/serger models:
560, 560ED, 560EDT, 800, 900