Minimal 1-1/2" diameter, 2-1/2" deep. Can be installed in a range of locations. Access to back of ceiling is not needed.
Mounts to Tech Lighting aG's special cylindrical 11/2" diameter, 21/ 2" deep junction box (included). Access to back of ceiling is not needed. If wall mounting, head should be no longer than 6".
For use with remote transformer and any Free Jack pendant or head (sold separately).