Both sides of a flat bastard file have double cut teeth.
Length of hacksaw blade is measured from Centre of one pin hole to the centre of other pin hole.
Safe edge of a file tool is one which is not having any teeth's cut on it.
During filing, sometimes the metal chips (filings) will clog between the teeth of files. This is known as ‘pinning’ of files.
Files which are pinned will produce scratches on the surface being filed, and also will not bite well. Pinning of the files is removed by using a file brush also called a file card, with either forward or backward stroke.