Mechanical pencil lead refills 0.3mm, 0.5mm, 0.7mm & 0.9mm lead are 60mm in length. This is a standard length & diameter and any brand of lead can be used in a mechanical pencil with the same diameter.
0.3mm / 0.35mm lead and 0.9mm / 1.0mm lead are the same size (just rounded down) so you can use either size in pencils that have one of these two diameters.
Mechanical pencil lead refills 1.4mm, 2.0mm, 3.0mm, 3.15mm and 5.6mm the length of the lead can vary between different manufacturers. However if you want to try a different brand you can usually cut it down if it is too long.
Pencils are graded on hardness and blackness H & B in a range from 9H a hard lead that makes light grey coloured lines to 9B a very soft lead that makes dark black lines. The standard writing pencils uses HB lead which is in the middle of the range.