There is a kit at demon tweaks with all the bits in it specially made for a Caterham - fits both Rover or Ford engines - I should imagine you could get it cheaper if you bought the individual bits, although through motor factors, but I went for this as I wanted to get it sorted quickly- also gauge doesn't look that out of place against the orginal VDO gauges on my car. https://www.demon-tweeks.com/uk/search/shop-by/q/caterham%20mechnical%20oil%20pressure%20gauge/ I also thought it might come with some sort instruction, but alas no, hence my initial enquiry.