"Bought 4 of these windows-very good value for the money...o/a size includes 40mm header/vent and 20mm sill-both are not essential.No contact info with instructions-hence this review. height and width extensions are available apparently-I couldnt source any. the end caps for header and sill ends are supposed to clip in,with a smear of silicone to seal. The caps supplied did not,and were a constant p.i.t.a. being dislodged during fitting. loads of spacers and securing brackets supplied. No information on removing the internal beads. Overall appearance is good,as was delivery-a lot quicker than advertised."