These vents are 455mm long 

These vents can be screwed or clipped to the window
The internal part can be opened to provide air flow upwards or downwards 

Internal vent size H 18.5mm L 455mm D15mm
External vent size H 18.5mm L 455mm D25mm
 Outside Hole Centres Is 435mm with one centre hole 

• Equivalent Area: 5000mm2 EQA
• Free Area: 5049mm2 
• Acoustic D n,e,w (+/-) - vent open: 35(0;1)
 • Acoustic D n,e,w (+/-) - vent closed: 43 (0;0) 
• Air Leakage: 1.29 m3/h 0.36 L/s 
• Water tightness Test to BS EN 13141-1: Resistant to water penetration using method 1A meeting Class 9A requirement up to and at 600pa in BS EN 12208 
• DB Rating: Airborne sound insulation to BS EN ISO 10140-1:2016 Annex E and BS EN ISO 10140-2:2010 and single number calculated in accordance with BS EN ISO 717-1:2013