These washers made of heat-resistant Mylar(TM) can be used instead of high pressure silicone grease in ultrasonic stack joints.
High pressure silicone grease probably does the best job of "wetting" the surfaces for good coupling and low acoustic losses, but it is much harder to train somebody to apply the grease correctly than it is to use a fresh washer each time the tooling is assembled. Also, silicone can interfere with decorating operations such as printing or painting, and is therefore banned from some plants.
To select the correct washer, measure the stud diameter and use the next larger ID, then measure the diameter (or diagonal) of the faces in contact, and use the next larger OD. If your OD is larger than the 46 mm, use 46 mm OD.
IMPORTANT: Use a new washer each time the tooling is reassembled. Do not use both grease and a washer in the same joint.
Washers come 35 to a pack. Order the number of packs you want, not the number of washers.