The Mullard (Philips) CL8630 gunn oscillator module has a rated output of 17 mW and is a model of good design. The flange mates with WG 16 but the cavity is deliberately made smaller than WG 16. This step has a similar effect to the iris in other modules such as the American Solfan.
When current it was noted that the CL8630 was quite immune to hands passing close by the cavity when in operation. Most designs exhibited a frequency shift when approached.
The module flange is 41 mm square and matches WG 16. The module measures 20 x 16 mm and is 45 mm long. The internal cavity dimensions are 15.6 x 7.78 mm.