The Vernier Dynamics System (VDS, discontinued) and Mass for Dynamics Cart (MASS) each include a mass with the correct hardware for attachment to a Vernier cart.

Here is a photo showing how the included long hex nut bolt is used to attach an accelerometer along with the Vernier mass included with Vernier Dynamics System (VDS, discontinued) and Mass for Dynamics Cart (MASS).

Also attached is a photo showing how to attach the Vernier mass included in conjunction with the Dual-Range Force Sensor (DFS-BTA) and the Low-g Accelerometer (LGA-BTA).

See also How do I put the Vernier Dynamics System mass and the dual range force sensor on the green metal dynamics cart at the same time?

If you are missing any of the mounting hardware, it is available as Fasteners for Dual-Range Force Sensor and Accelerometer (ACC-VDS).