//prepare transformation of mate
Matrix3D oTransformation = new Matrix3D();
oTransformation.OffsetX = 20.0;
oTransformation.OffsetY = 20.0;
oTransformation.OffsetZ = 0.0;

//prepare description of mate
Eplan.EplApi.Base.MultiLangString oDescription = new Eplan.EplApi.Base.MultiLangString();
oDescription.AddString(ISOCode.Language.L_en_US, "User defined mounting point number 001.");

//create new point mate object
MountingPointMate oMountingPointMate = new MountingPointMate();
oMountingPointMate.Create("UserMate001", oDescription, oTransformation);

//assign mate to 3D placement
oMP.AddMatePersistent(oMountingPointMate);

//find the new mate
Mate oUserMate001 = oMP.FindTargetMate("UserMate001", false);

//remove the mate
oUserMate001.Remove();

//oPlane.FindTargetMate("UserMate001", false) == null