Here's the best place to get one. Just give them the serial number of your bass and they'll send you out the right one.
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Regarding RIC's 4003/S5 string bass, this is a very nice and unique bass! The interesting part is that they use a 1/16" wider neck than the standard 4003 33 1/4" scale neck and cram 5 strings onto it. String spacing is a little tight but not overly tight. RIC use a 115 gauge string for the low B, (most 5-string manufacturers use a 130-135 gauge B string) The 115 gauge string is tight and doesn't flop, and produces a excellent low B on this bass. Standard RIC string gauge on the bass are; 45,55,75,105,115 which make this bass sound great. Combine these strings with the 6-pole toaster neck p/u and 5 pole bridge p/u wired in mono (no third capacitor here) and this bass sings.
If your a Rickenbacker owner and in the market for a 5-string bass, check out a 4003/S5. You won't be sorry.
Cheers