second and third pane maintained in a spaced apart thermally insulated relationship by a sealing strip 23 triple glass panels are also well known and serve to increase the thermal insulating capabilities of the window between the outside o and inside i of the window hence the present invention contemplates the use of a universal adaptor 25 to modify the effective opening between the frame members 11 and 12 of the window frame 10 to receive a triple glass panel 20 the adaptor 25 is a unitary structure of a substantially rigid insulating material such as vinyl in a first embodiment fig2 and 4 the adaptor includes a base 26 and a first portion 27 depending downwardly therefrom the first portion 27 includes a first downwardly depending leg 28 having an external shoulder 29 and a second downwardly depending leg 30 spaced apart from leg 28 leg 30 is recessed to provide an inwardly extending shoulder as at 31 and then continues in a downwardly extending leg portion 32 a cross support 35 joins leg 28 to the portion 32 of the leg 30 the shoulders 29 and 31 limit the depth of insertion of the adaptor into the frame 10 as illustrated in greater.