Multiple INNER JOIN from the same table

You should specify different aliases for your tables . you are calling all of them m.

SELECT m1.MetalCode as 'Metal1', m2.MetalCode as 'Metal2',m3.MetalCode as 'Metal3'
FROM Item as k
INNER JOIN Metals AS m1 ON m1.metalID=k.metal1 
INNER JOIN Metals AS m2 ON m2.metalID=k.metal2
INNER JOIN Metals AS m3 ON m3.metalID=k.metal3
WHERE k.ItemID=?

try this:

SELECT m.MetalCode as 'Metal1', n.MetalCode as 'Metal2'o.MetalCode as 'Metal3'
FROM Item as k INNER JOIN Metals AS m ON m.metalID=k.metal1 
        INNER JOIN Metals AS n ON n.metalID=k.metal2
        INNER JOIN Metals AS o ON o.metalID=k.metal3
WHERE k.ItemID=?

Well, not completely wrong. ;)

Wherever you have "INNER JOIN Metals AS m", m needs to be something unique (not m every time).

Try something like this (not tested):

SELECT m1.MetalCode as 'Metal1', m2.MetalCode as 'Metal2', m3.MetalCode as 'Metal3'
FROM Item as k
INNER JOIN Metals AS m1 ON m1.metalID=k.metal1 
INNER JOIN Metals AS m2 ON m2.metalID=k.metal2
INNER JOIN Metals AS m3 ON m3.metalID=k.metal3
WHERE k.ItemID=?