Each of the letter sequences below can be found in two related words.  For example, given the clue 
PEA, the two words would be PEAR and PEACH - both fruits.

1  EVEN
2. OUN
3. OPA
4. RON

HINTS:
1. Numbers
2. Weights
3. Gems
4. Metals

Answers:

1. SEVEN - ELEVEN
2. OUNCE - POUND
3. OPAL - TOPAZ
4. IRON - BRONZE