Dog collars
A collar is the most demanding piece a beginner attempts, because it has to fit a moving animal and hold under load.
Measuring
Measure the neck where the collar will sit, with two fingers under the tape. Add the buckle length. For a growing dog or a thick winter coat, build an adjustable version rather than guessing.
Fixed or adjustable
A fixed collar is faster to build and neater to look at. An adjustable collar uses a tri-glide and a longer webbing section, and it survives a change of season without being remade.
Hardware
Match every part to one width. A nineteen millimetre buckle, nineteen millimetre webbing and a nineteen millimetre tri-glide, or the collar will twist. Metal for large dogs, plastic for small ones and for cats, where a safety release is essential.
Buying
Collar kits with all the parts in one set are listed here: dog collar kits (https://www.123paracord.co.uk/diy-kits/dog-collars/).