Part numbering - Panasonic M series ECA-1CM331BJ

What does the suffix J call out in Panasonic M series capacitor, such as ECA-1CM331BJ

The J at the end is not really standard so it does not always appear on the datasheet but will appear on the full specs (which are not available online). Some of the bulk parts come with a 3.5mm lead space. Because of that there is no way to move to T/B product without changing your board as the default lead spacing for taped product would be 5mm – so they came up with a part number to have 3.5mm lead spacing for T/B, that is what the J at the end calls out.