A reaction vessel support device for mounting on a magnetic stirrer hotplate. The modular device comprises a base unit capable of positioning and seating at the reaction hotplate, and an insert formed non-integrally with the base unit comprising a reaction vessel receiving portion capable of seating and locating about a portion of a reaction vessel. At any one time, the base unit is capable of accommodating a plurality of different shaped and sized inserts each insert being configured to seat and support a specific reaction vessel of particular shape and size. The device therefore serves as a magnetic stirrer hotplate adapter.