They should be interchangeable and both fit the shock body ... there are replacement metal caps for the 5/6 series with the 3mm hardware bushings, so I don't know if you have those or if they are the caps used on the 4/SC10 series that uses the 4-40 hardware ... the earlier Big Bore's usually came stock with the gold shafts and the bottom eyelets were anodized blue aluminum, the aluminum caps on those used the little orange/red O-rings and tended to want to 'tear' if used a lot ... I prefer the plastic caps with the recessed bleeder screw that uses the little clear/white plastic washer under the screw, they tend to be a little easier on the O-Ring under the cap too, but then I work a lot with the shocks apart and bleeding them ...