Suggestion, when you get it, take one off and take to an auto parts store and get one like it. In 10 years of Winnebago trailer camping, I have never lost one. The normal size is 1/2" x 20. Happy Camping.
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Ken and Joyce
2017 RAM 1500 Lone Star Quad Cab 5.7 Hemi, 8 speed, 3.21, Tekonsha P3
2018 Winnebago Minnie 2250DS, Haloview MC7108