Hi Laura. This looks like either a S351-14 or S390-14.The only difference between these two balance Series is the 'depth' of the bottom nylon shoe. The depth is the measurement from the heel-to-toe of the shoe at its widest point, just beneath and perpendicular to where the metal channel ends. The Series 351 bottom nylon shoe has a depth of 1", whereas the Series 390 bottom nylon shoe has a depth of 1-1/8". Compare with your old balances and see what you think matches best. I personally am leaning towards the Series 390, but photos can be deceiving. If it's over 1" at all though, the S390-14 is the way to go.
Your stamp code of 1390 is from an old rating system we no longer use. Weigh your window sash. You can then match that exact weight with one of the weight ranges listed alongside each stamp option on the product page.
