The T100 chain opener is the standard size required for the majority of applications. The mechanism will open the vent 250mm. If the sashes (side hung or top hung) are more than 1000mm high / wide then 2 chain openers should be fitted to ensure a tight seal is obtained upon closure. The minimum window height to enable full 250mm travel is 500mm. Allow for 300mm of conduit for the spent travel of the inner cable. All of the operators shown on this page will work with this opener.T100 250mm Chain Opener