Fender bullet truss rod allen size?

[Wehner]

I recently bought a 1975 Fender Jazz sporting the bullet truss rod. Needing to adjust it a bit, I wonder, which size allen wrench would I use?

[JustDavid]

Were it me, I'd just grab a cheap set of hex keys (should be Imperial, not Metric) & go for it. $5 max, & it saves you dragging the bass to a hardware store.