For metal- depending on the shape or size of it is best cut using a specific metal saw.
I'd a number of sleeves to cut in 2mm thick brass tubing, at about 25mm diameter. as sleeves for some door knob handles Tried the hacksaw and made a complete 4r5e of it, really bad, and im kind of used to cutting straight, but these were only fit for the bin.
I've an angle grinder and saw some info on YT about cheap cutting stands to hold the grinder, complete with adjustable vices and eventually bought one, though must say i was put off by how cheap they were and i associated cheap with nasty.
Night and day. The cuts, after a few to align were perfect, and the safety aspect (especially using a grinder) was well appreciated.
The stand cost me £15 on ebay new, of mass production but dont let that put you off, it is totally fit for purpose, makes the job a breeze and again as safe as houses.
Obviously there are limits to the sizes it can cut, but the fact it holds it straight and accurate is well worth buying.
You didnt say the size you need cut, but if its not too big, id recommend this stand, and although its for a 4 1/2", there will be something similar for a 9"