One of my amps - like many Fender amps - has the input jack on the top. I may not use it for weeks at a time, and I sometimes worry about dust getting in and "fouling things up". So, the other day I started googling 1/4 jack dust caps. Lots of options, lots of odd results, but nothing that really looked like what I wanted. Meh - live to search another day. I was walking through the kitchen, and saw a 2-liter bottle in the trash with a black cap. Hmmm, take off the cap, give it a quick wash, and just set it over the input jack. Voila! It's amazing the obvious options that present themselves when you don't overthink a problem.