This is 26.5mm diameter cds.
Manning states this as RRRR. (page77) with date range 1 Sep-31 May 1913.
Cowan & Dell say C = common, & date the cds from 18 Aug 1912 to 1965.
a discrepency(?), but a lovely strike dated 7/11/1910 is available here!
QLD DRILLHAM
$15.00Price