1964 Ireland Postal Stationery green  1/5 Shilling Registered Envelope Size H ( EU 8cHI,2).  Reverse of envelope has purple Minimum registration box removed, no red text, hence "c" designation.  the length of the text defines this as HI,2 ie length of LITIR CHLARAITHE is 49mm and length o f "THIS LETTER .... POST OFFICE" is 106mm, comma behind amounts on line 12