No. You can actually contact Vortex directly and they can provide you with a new flip cap for your Spitfire 3X Gen I. Their contact information is linked below:
https://vortexoptics.com/contactus
No, this Vortex StrikeFire II Objective Flip Cap is designed specifically for the Vortex Strikefire II red dot sight. You would need the Vortex Defender Flip-Cap, found by using the link below:
https://www.opticsplanet.com/vortex-defender-objective-flip-caps.html?_iv_objective-lens-diameter=56-mm&_iv_outer-diameter-699615208=range-41-dot-5-46-mm
This cap is meant for the Vortex Strike Fire. You will want to use FC-3 found on the following page instead:
https://www.opticsplanet.com/vortex-rifle-scope-flip-cap-cover.html
MPN: FC-3
This is just a single flip cap that is meant specifically for the Vortex Strike Fire. The Spitfire comes with flip caps and if you need replacements Vortex recommends reaching out to them directly.