This 3D model was originally created with Sketchup 8 and then converted to all other 3D formats. Native format is .skp 3dsmax scene is 3ds Max 2016 version, rendered with Vray 3.00 In attempting the transit of pipe through a double skin brick wall, I devised this 'collar' which should require just an additional plate to bridge the cavity if it is to be filled, and bolts/threaded rod to fix it - in as much it could be interchangeable or at least serviceable, but at the very least means the flue is a separate entity so if the stove is changed/uninstalled, this component can be adapted for another size pipe or simply stopped up with minimal extra materials.

As such it is a concept, there is no proof of concept, nor does the material dimensions & texture fill truly represent the thickness and type intended, it's merely shown to be aluminium because that's the only continual plane surface metal, while 5mm thickness ensures the model does not show background elements, so these are entirely subject to change pending a professional opinion regarding the model as a viable way to install a flue through a wall - i.e. the wall isn't built yet, so if this is deemed a good way to install a flue, it can be built in and achieve an exact fit, which may be the vital prerequisite....