The 755PFM has the following dimensions.
Visible Depth: 23mm
Recessed Depth: 79mm
Hole Cut Out: 90mm (suits 3.5' Holesaw)
Cable Range: 1.00mm to 2.5mm with up to three conductors per terminal, allowing daisy chain operations of upto 40 alarms over 150 Metres
For further information on this product please visit http://www.clipsal.com/Trade/Products/ProductDetail?catno=755PFM