you need to take out the beads (i.e the plastic strips which hold the glass unit in place).
if it is internally glazed simply take out the beads using a thin strong scraper
if externally glazed first take out the rubber gasket from the inside of the window then the beads from the outside. if a double-sided glazing tape is used instead of a gasket then this will need to be cut first. n.b. if this is so you will need to replace the tape. 6mm tape is the thickness i have used but thicknesses vary.
once glass is out measure h+w plus thickness of unit. thicknesses vary in increments of 2mm (18,20,22,24,28mms). also check if the unit is toughened or not, there will be a kite mark in one of the corners if it is.
knob-free, March 2009
