The Mass for Dynamics Cart (MASS) includes a mass with the correct hardware for attachment to a metal (VDS) dynamics cart.

Here is a photo showing how the included long hex nut bolt (included with the Mass) is used to attach an accelerometer along with the Vernier mass.

And here is the image with the Mass shown attached to the cart with both a force sensor and an accelerometer.

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).