Rapid Accessory Changing
These quick change handpieces have a unique
push/pull collet chuck release mechanism.
Wait for the motor, flexible shaft and accessory to come to
a full stop before opening the chuck. Then, pull the outer grip
forward with one hand while holding the back of the handpiece
with the other. Remove the accessory and insert the shank of the new one at least 1" (25mm) into the chuck.
Pull the grip all the way back until the chuck snaps closed.
https://www.foredom.net/wp-content/uploads/handpc_instructio ns/53_discontinued.pdf