Unit Insert Molds:

Unit insert molds are mold inserts that utilize a common frame.  The mold inserts mount into the common frame by a variety of methods.  The frame typically stays mounted in the molding machine.  There are a few standards for unit inserts suck as Master Unit Die, Round Mate.

The advantage of unit inserts is lower cost and typically faster build time.  The disadvantage is that, to move the mold to another molder, it may be necessary to purchase the frame and thus negating the original cost savings. 

For the molder they offer faster mold changes.

It is important when purchasing a mold as a unit insert to make sure it is made by a common standard and not a custom or proprietary insert. 

Free Stand Molds:

Free stand molds are the most common type of mold.  The mold frame and mold plates are all included in the design.  They can be readily moved to any molding machine that fits the mold size.  They can have longer lead times and be more expensive to build.