performs simple boolean operations on two triangle models. These models can be any triangle model and not just triangle primitives.The Boolean Triangles button performs simple boolean operations on two triangle models. These models can be any triangle model and not just triangle primitives.
Performing boolean operations on two triangle models creates a new trimmed triangle model.
Since you specify a tolerance you don't get a completely watertight model after performing boolean operations. The model is accurate enough for machining, but if you want to use the model for STL rapid prototyping you must use the Auto Stitch 
functionality available from the Triangle Fixing 
toolbar.
The options on the Boolean Triangle dialog box are shown using two overlapping blocks.
ADD the triangle models - adds two triangle models together.
A new model is created with the name of the two models and the boolean operation. So, if the blocks are called Block and Block#2 the new model will be called Block#2 - ADD - Block where Block#2 is the primary model and Block the secondary.
REMOVE from the triangle model - subtracts the secondary triangle model (the one selected in the Secondary triangle model area of the dialog box) from the active model (the one preceded by > and in bold in the Explorer).
Rotating the model you can see it more clearly.
The new model will be called something like Block#2 - REMOVE - Block.
INTERSECT the triangle models - creates a new model of the intersection (or overlap) of the two triangle models.
The new model will be called something like Block#2 - INTERSECT - Block.
Secondary triangle model - select the secondary triangle model from the pull-down list. All models except the active model (which is the primary model) are displayed in this pull-down list.
In this case you can see that Block#2 is not listed as it is the primary model.
Options - Tolerance - determines the accuracy to which the intersection is constructed.
See also:
Triangle Modelling Improvements
