US 97430878 A description for purposes of illustration the invention is shown in the drawings in conjunction with a heating assembly in which a heating tube 10 is disposed in a heat treating furnace 11 whose top bottom and side walls 12 13 and 14 define a chamber 15 in which workpieces not shown are placed for treatment each heating tube 10 is made of a refractory ceramic material and is formed with an open upper end and a closed lower end the upper end portion of each tube projects loosely through an opening 16 fig1 in the top wall 12 of the furnace 11 and is insulated with respect to the top wall by ceramic wool 17 or the like which is packed into the opening extending around the upper end portion of each tube is a ceramic collar 18 fig1 which is attached to the tube by a strong heat resistant cement angularly spaced studs 19 extend upwardly from the top wall 12 of the furnace and project through radially extending slots 20 formed in the collar 18 the collar being clamped against the top wall 12 by means of nuts 22 on the upper ends of the studs heating of each.