Round Windows

ZEROplus’s Lo-FP range of round windows is available in three diameters:

  • Lo-FP-12 suits a 305mm diameter door cut-out
  • Lo-FP-18 suits a 457mm diameter door cut-out
  • Lo-FP-24 suits a 610mm diameter door cut-out
Round window frames: porthole windows, circular vision frames for doors, walls and partitions

All three porthole window sizes are easy to install and provide a low profile, ‘flush to the door’ look. Sheet metal screws pass through the door cut-out, and fasten to the opposite side of the circular vision frame. This eliminates the need to drill the door for through bolts, saving installation time and labour.

With the corridor side of the frame free of fasteners, the Lo-FP range of round window frames is cleaner, sleeker and more secure. Special security fasteners are also available.


The Lo-FP round window frames are 20GA cold-rolled steel, and grades 304 and 316 stainless steel.


Our round window frames are zinc-plated, grey primed and stainless steel as standard. Other finishes are available to special order.


The smooth round contour of ZEROplus’s low-profile frame style is sleek and clean, giving any setting a unique look and feel.


Our round window frames are fire tested to four hours on steel doors and one hour on timber doors when used with Zero FS2002 intumescent glazing tape and FS4004 aperture liner (on timber doors) with suitable glass. FS9009 ‘ceramic type‘ tape is also suitable for use on fire-rated steel doors.


The Lo-FP round window range is now available in two profiles to suit standard 6mm glass (Profiles AA1), and 22-25mm double glazed units (profiles BB1) on standard 44mm thick doors.

Unlike the Slimport porthole window designs which fix through the bevel and have two different halves, Lo-FP round windows consist of two similar halves which fix through the flat face of the porthole. This means the glazing pocket will increase in direct proportion to the door thickness. So if you add 10mm to the door thickness, you also add 10mm to the glazing pocket. All that will be required is longer screws for fixing.


Take a look at the full product details and catalogue, or phone +44 (0) 1785 282910 for assistance.