Description: The Reverse Retrofit version is for use on single hung windows where there is insufficient room on the top sash to install any other version. The units are single action, so fitting one either side of the window frame ensures compliance with ASTM F2090 A Dimension 13/64" to 15/64". Color White. Reverse Retrofit Angel Ventlock, Single Action. The Reverse Retrofit Angel Ventlock is the ideal limit control device in aftermarket applications. This Window Opening Control Device (WOCD) can be mounted on a vinyl, wood or aluminum single hung or double hung window. Made of Stamped Steel with Stainless Steel Pin and Spring. The Reverse Retrofit Angel Ventlock version attaches to the window frame and must be mounted to restrict the sash opening to less than four inches. These units are single action, so installing one on either side of the window frame ensures compliance with the code ASTM F2090-2008 and 2010. These reverse retrofit angel ventlocks are packed with installation hardware and sold in Pairs (Left Right). Fits on Pella windows. Also known as Window Opening Control Device for Double Hung Single Hung Windows. Installation Instructions included.