For plug-ins that will forever be internal to your site use the constructor that takes a single unsigned int parameter. The numeric range 0 - 0x7ffff (524288 ids) has been reserved for such plug-ins.

The example plug-ins provided with Maya in the plug-in development kit will use ids in the range 0x80000 - 0xfffff (524288 ids). If you customize one of these example plug-ins, you should change the id to avoid future conflicts.

Plug-ins that are intended to be shared between sites will need to have a globally unique id. The Autodesk Developer Network (ADN) will provide such id's in blocks of 256. You will be assigned one or more 24-bit prefixes. Once this has been obtained, used the MTypeId constructor that takes 2 unsigned int parameters. The prefix goes in the first parameter, and you are responsible for managing the allocation of the 256 ids that go into the second parameter.

Example: 0x00118380, 0x00116605 are registered by internal people @ Autodesk.