RhinoCommon API
BrepMergeBreps Method | 
            Combines two or more breps into one. A merge is like a boolean union that keeps the inside pieces. This
            function creates non-manifold Breps which in general are unusual in Rhino. You may want to consider using
            JoinBreps or CreateBooleanUnion functions instead.
            
Namespace: Rhino.Geometry
Assembly: RhinoCommon (in RhinoCommon.dll)
public static Brep MergeBreps( IEnumerable<Brep> brepsToMerge, double tolerance )
Public Shared Function MergeBreps ( brepsToMerge As IEnumerable(Of Brep), tolerance As Double ) As Brep
Parameters
- brepsToMerge
 - Type: System.Collections.GenericIEnumerableBrep
must contain more than one Brep. - tolerance
 - Type: SystemDouble
the tolerance to use when merging. 
Return Value
Type: BrepSingle merged Brep on success. Null on error.