Poor BEX 288 - Flying Horse will mislead you. On A.C.s with a Bristol engine the Vokes Oil Filter was raised, to clear the chassis, by Thames Ditton adding an alloy extension piece. The shape of this was exactly like a dog's bone and it was inevitably so named.
On the top of The Dog's Bone is a tapped hole which had a brass blanking plug fitted if there was no oil temperature gauge on the car. If the gauge was fitted the 3/8" BSP brass plug was replaced with a male/male threaded spigot which then accepted the Smith's temperature bulb.
Sadly most cars have lost their Dog's Bone extensions by reason of giving up on Vokes and accepting a modern spin on cannister. In this case you will find a spare tapped hole on the port rear corner of the Bristol sump as described by Graham Flying Horse for the 400.
Should you be at The International I will show you what I am rambling on about beneath LM5000's bonnet.
All of which takes us back to the recent postings on production of more Vokes Insert Assemblies .....