Choosing 'offset' will mean the taper has at least 1 flat side no matter what the dimensions (see fig 3). However if one dimension from the larger end is the same as one dimension from the smaller end, the taper will have 3 flat sides (see fig 4).
Length
The overall length of the taper will be determined by us according to standardized ductwork specification regarding airflow. Please let us know when ordering if you would like to overide this by specifying the length.
Joint Method
You can choose the method by which you would like to join the duct. Selecting 'flanges' will mean that the duct is supplied with ready fixed 'Doby' flanges on either end. These flanges enable the duct to be joined by simply bolting it together - one M8 nut and bolt on each corner. Nuts and bolts are available in the Fixings & Supports section.
Selecting 'flanges loose' will mean, as is suggested, that flanges will be supplied but not fixed to the duct. They can be fixed on with rivets or screws as part of the installation process.
Alternatively, selecting 'slip-joints' will mean the duct will be supplied with the ends fashioned in such a way that they slip one inside the other to a depth of 50mm. They can then be fixed with either drill-screws or rivets, and sealed with sealant or tape.
Selecting 'nothing' will mean the ends will be plain, as in the drawing on the product page.