I beleive you want these fittings. They are solder on pipe nipples with nuts.
I can’t remember if you need the 1/4” nipple for 1/4” BSP with 1/4” tube or 5/16” tube. The nipple and nut stay the same but the tube can be different sizes.
https://www.vintagecarparts.co.uk/pr...nut-and-nipple
I also used these fittings for hooking up the oil cooler lines. Although I think they were sized for 1/2” tube.
Last piece of advice when making these lines up. Put the nut on with the female end facing towards the end. Then solder on the nipple. If you forget the nut it’s easier to fix then the flared fittings.