denchen
Gold Member
Im no expert. but a British Standard Pipe, thread is always referred to the size of the hole of the pipe it serves. A 1/8th BSP will be for pipe with a 1/8th inch hole in the pipe, but for tapping the thread you need to drill something like 8,8mm if memory serves me right. A lot of the old grease nipples used to be 1/8 BSP but the treaded hole was about 3/8th inch.