Mulling system for plural fenestration assemblies with matching thermally broken joining plates that have rotated and engaged arrangement across mulling axis

A mulling system for a plurality of fenestration units comprising:

• a first joining plate that extends longitudinally along a mulling axis, the first joining plate configured to attach to a first outer edge of a first fenestration unit, the first joining plate including a first alignment fin configured to be received in a first groove of the first fenestration unit, the first joining plate including a first plate member, a second plate member, and a first thermal breaker that extend longitudinally along the mulling axis with the first thermal breaker attaching the first and second plate members;
• a second joining plate that extends longitudinally along the mulling axis, the second joining plate configured to attach to a second outer edge of a second fenestration unit, the second joining plate including a second alignment fin configured to be received in a second groove of the second fenestration unit, the second joining plate including a third plate member, a fourth plate member, and a second thermal breaker that extend longitudinally along the mulling axis with the second thermal breaker attaching the third and fourth plate members;
• the second joining plate configured to attach to the first joining plate to join together the first fenestration unit and the second fenestration unit with the mulling axis extending between the first joining plate and the second joining plate;
• the first joining plate substantially matching the second joining plate to define a corresponding rotated and engaged arrangement of the first joining plate and the second joining plate across the mulling axis;
• wherein, in the rotated and engaged arrangement, the first thermal breaker aligns with and overlaps the first alignment fin along a first transverse axis extending perpendicular to the mulling axis from one side thereof;
• and
• wherein, in the rotated and engaged arrangement, the second thermal breaker aligns with and overlaps the second alignment fin along a second transverse axis extending perpendicular to the mulling axis from an opposite side thereof.