The '0' size is one of my favourite types of stove. The Optimus version seems to be less commonly encountered than those made by Primus. This example is mid-way between the 2 already in the reference gallery collection in terms of date and features. This example is fully original with the sole exception of the trivet ring which, although of a pattern which was available from Optimus, is, in this case, marked 'Radius'. The tank base provenance marking, dimpled spirit cup, pressure release key and original burner are all identical to those produced in the 1920s: The changed feature since the 1920s was the plainer filler cap top, which had replaced the 'sail' type cap between 1930 and 1932 (as evidenced by comparing the 1929 and 1932 catalogue parts sections): Later in the 1930s the dimpled spirit cup was dropped in favour of a plain ring and the base marking and burner top designs changed too as can be seen in this example (link) from c.1939.