What Is This Thing?

It WAS on the tongue of my Ranger trailer. It appears to cover the hydraulic port for the surge brakes. I assume someone helped themselves to MINE at the ramp last weekend. I need to replace it but I'd like to know if it has a real name to make my search easier. Anyone?

Master Cylinder cap

whoever took it may they leave it loose and it fly off at 70mph and put a hole in their boat.

Thank you!

Agreed.

Here's one

https://www.amazon.com/UFP-Brake-Lockout-Cap-Upgrade/dp/B006UH5ZSY

OK...so I guess I have to admit it...I'm totally mechanically incompetent. I have the replacement in hand....WHY WON'T IT install right? Is there some sort of trick to get these suckers in right? I see the little notches and the teeth....I aligned them up...all is well...except for the fact it won't "TWIST" into place the way it should.....[censored] am I missing? I'm ready to start throwing [censored]! HELP!

+1000 and they get spinal meningitis, their a$$hole draws up around their nose, they get the drizzling $hits and live to be 1000 years old.

Best idea I can give you is go to either Rockwall Marine or Plano Marine and ask for help. Both places have helped me many times with similar issues.

You may have to bleed the system, I'm a skeeter guy we have a different system but if takes fluid, and it's been compromised by driving and activation while stopping. You may want to heed GIG'UMs advice.. jm2c's

Make sure the tongue is pulled out. It goes in a specific way. The cap is designed to twist and lock out the brake system.

Put it in purpendicular to the tongue, the twist. It will lock in place. To lock out the brake acuator or remove, push button the turn again..