Flare nut wrenches are specially made to fit over steel brake and fuel ines to tighten the small nuts compressing the flared ends.
Flare nut wrenches are used on fuel lines. Regular sockets are used on head bolts.
Flare nut wrenches are just small wrenches, usually 5/16 or similar with a slot to pass over the pipe.
A flare wrench, also known as a flare-nut wrench, tube wrench or line wrench is used for gripping the nuts on the ends of tubes (like automotive brake lines and household plumbing). It is similar to a box-end wrench but, instead of encircling the nut completely, it has a narrow opening just wide enough to allow the wrench to fit over the tube. This allows for maximum contact on plumbing nuts, which are typically softer metals and therefore more prone to damage from open-ended wrenches. See images of flare nut wrenches by searching google and see what purchase links pop up. Cheers
A retaining nut could be the packing gland nut on a valve stem or the nut used on a flare or compression fitting
A flare joint is used on gas fittings and uses a nut and flare fitting to make the connection. This is a dry fit with no joint compound. The copper is soft enough that it compresses with the nut and forms the seal.
Flare nut
A wrench is used to tighten nuts. Socket wrenches are a type of nut driver.
Wrenches or spanners are most useful. Sockets are very useful in many cases. I keep complete sets of both SAE and Metric wrenches in my car. along with Allen wrenches of both types. I do have some excellent adjustable ( crescent ) wrenches, but prefer wrenches that fit exactly as I was taught in maintaining aircreft.
I would buy a set of flare nut wrenches. They have an open side to fit over the line so that you can get on the flare nut going into the transmission and radiator. Get a pan to catch the tranny fluid that is going to run out when you break the lines. There are 2 lines going into the tranny and 2 lines going into the radiator. Before you take the lines loose identify their position on the radiator and tranny with masking tape.
Humans have improved the simple wrench by making box wrenches, off-set wrenches and ratchet wrenches. An indirect improvement was the invention of sockets, so the head of a bolt or nut could be totally gripped.
When you use soft copper tubing, you flare the end to make the connection. You put a nut on the tube and then flare the end so that it looks like a funnel. Then you can connect the tube to a fitting and when you tighten the nut it compresses the copper and makes a seal.
The are most used in engineering, garages, plumbers some electricians construction and in the home for DIY - Basically anywhere where a nut/bolt configuration is required even maccano