Conical 4" (10.2 cm) neck for use with 6475, 6476, 6477, 6479, 6480, 6481, 6491, 6492, 6497, 6498 and 9656 ACE Reaction Flasks. Supplied with three outer joints in line, plus a thermometer side arm which is internally threaded for use with 5029 Nylon B