To allow a tight fit, the guiding rails in the adapter are built as narrow as possible. This may cause initial problems when mounting the adapter first time. Push the adapter firm but gentle on your VA-1 angle finder. It may be necessary to clean the guiding rail with a needle or small screwdriver to remove excessive printing powder.
After a few times, the adapter will slide smooth into the angle finder receptacle and still be tight enough to keep it securely mounted.
Pleas note, that all parts, even your VA-1, are built with small tolerances that may cause variations in the fit of adapter and angle finder.