For use with vertical terminations only. Cap features twist lock collar & grid to keep birds out. Designed for stoves that burn wood pellets. Patent pending venting for stoves & inserts that use wood pellets. Ul listed for 3" clearance to combustibles in the USA & Canada. 3" Round For use with vertical terminations only Cap features twist lock collar & grid to keep birds out Designed for stoves that burn wood pellets Patent pending venting for stoves & inserts that use wood pellets Ul listed for 3" clearance to combustibles in the USA & Canada.