sorry yes 31mm festoon, edited that! was looking at my watch list on ebay and had some 42mm ones on there for some reason :confused:
i went with blue festoon lights
http://www.350z-uk.com/topic/59886-blue-festoon-dome-light-bulbs-anyone/page__hl__%22dome+light%22
be careful on the type you get as you dont want to bridge the gap between connectors and short the circuit can be a costly job, few threads on the forum about it