Guide updated on 18th April 2019 to recommend Bahco.
Guide updated on 14th October 2019 to remove the recommendation for a four-in-hand farrier's rasp as this is not hardened.
Guide updated on 11th November to recommend a bastard cut too.
A 12” (305mm) file is usually the longest length used in woodworking and metalworking, Paul recommends using a 10” (255mm) or 12” (305mm) flat file ideally with second cut (medium) teeth, but a bastard cut will work well too. The difference is simply the size of the teeth.
We purchased this Bahco 10” from Amazon in April 2019 for £15.49 and Paul uses it daily. He would recommend this as a first choice. This is also available on amazon.com