This article refers to the following products:
Dual-Range Force Sensor (DFS-BTA)
Go Direct^® Force and Acceleration Sensor (GDX-FOR)
Wireless Dynamics Sensor System (WDSS)

All three of these sensors have a hexagonal barrel, or standoff, extending from the sensor case. This part is firmly attached to the load cell with a tiny lock washer, and should not be removed. It is often reinstalled incorrectly, without the lock washer.

When installed without the lock washer, the sensor gives poor force readings, often much too large. This can be an issue when replacing a broken part, or when someone unscrews the hex standoff and loses the washer.

When driven too far into its threaded hole, the hexagonal barrel contacts with the structural member that includes the strain gage. It bumps up against it enough to create a faulty high force reading.

If the washer is missing, the extender threads go too far in and can cause problems. Tip: When re-attaching the hex extender to the body of the sensor, use pliers to attach it tightly. If it is only “finger tight”, there is a chance it will unscrew whenever anyone detaches the hook.

If the washer is missing, contact Vernier Technical Support to get a replacement.

You may also be able to find them at a local hardware store as a Steel Split Lock Washer – for Number 6 Socket Head Screws, 0.148″ ID, 0.216″ OD.
Also sold by McMaster:
http://www.mcmaster.com/#90073a007/=13zvdxd