HPS 5/8" (16mm) Black High Temperature 3-ply Reinforced Silicone Coolant Cap Bypass Heater, 1-5/8" Length, 350F Max. Temp, 4mm Wall Thickness

Good quality for heat. Nice fit.

Made with Great quality material.

Wish I could replace all the molded hoses on my FB with silicone hoses like this cap. Caps-off the hard pipe from the radiator.

Hah! The 5/8" I ordered/received is a quality product. It fit on the radiator and received the clamp nicely.Spend the extra few bucks for these, the standard rubber stuff you get is junk.

After wearing through multiple standard all rubber plug, discovers this nylon reinforced plug which should address the all rubber failures. Time will tell, but looks very promising.

Good stuff, won’t dry out and crack like OEM. Seals much better too. Grab it if your steam port on GM OBS radiator won’t seal or cap just needs to be replaced. Little expensive for what it is but works great!

I have an aftermarket northern radiator in my Chevelle and has a 5/8 bung on the top that isn’t used, came from the factory with a regular old cheep rubber cap that didn’t hold up, I kept replacing the cap every season with similar quality Dorman caps from the parts store but after a few runs and a few months the rubber ones get huge dry rot cracks all around and just never know when they’re gonna go so I keep a spare in the glove box, got fed up and found these. These caps are 110 times better than anything you’ll find in a parts store and appear as though they are in it for the long haul and will last years. Well worth the investment and sure beats being stuck on the side of the road with a coolant mess on your hands.

They look to be good quality. I'll buy more.