Hi Colin

Was this what you were looking for, it was Triplex not Pilkington

"TRIPLE ‘X’ Code.

Many of the older classic car veterans will know of the TRIPLEX glass code. TRIPLEX were the company the majority of UK car makers used to supply their motor cars window glass in the post war period. This glass is toughened and carries the British ‘kite’ mark. The actual etched in marks on the glass are the word ‘TRIPLEX’, with three ‘X’s in the centre underlined by the word ‘TOUGHENED’. Under that the kite mark might be placed. Specially toughened windscreen have the word ‘ZEBRAZONE’ where ‘TOUGHENED’ would be. This is a screen with a central ‘clear’ area when broken so the driver can still see through it.

The code is etched into the glass during manufacture by TRIPLEX. It assists in determining when the glass was made. This can lead to assisting to decide the age of a car, or more accurately the approximate age of the car. The two letters at each end of the word TRIPLEX, that is the ‘T’, ‘R’, ‘E’, and ‘X’, will have a small dot under one of them. These four letters equate to the quarters of the year; so T is for Jan, Feb and March; R is for April, May & June; E is for July, Aug and Sept; and X is for Oct, Nov and Dec. Both the words toughened and zebrazone have nine letters. The dot will appear under a letter indicating the year, No dot at all will be 1950 or 1960. The first letter which might be the T or the Z indicates 1, so it will be 1951 or 1961. Then the O or E will be 2, 1952 or 1962; then the U or B will be 3, and so on until the last letters of either D or E, indicating a 9.

So if a windscreen in a M.G. TD or YA/YB, or any other window, has a dot under the dot under the R in TRIPLEX, and another under the T in TOUGHENDED, ( or the Z in ZEBRAZONE), this would indicate it was made in the first quarter of 1951. So cars for approximately the first six months of 1951 might have those indicators. If the same dots appeared in the same places, but on a MGA or Mk3 Magnette, or a Midget, it might be a 1961 model, with glass from the first quarter. Try your own car and see if it works.

If someone has restored the car, or it has had a broken windscreen at some time, you need to check all the windows to eliminate any error. Few cars get side or rear windows broken."