Sometimes I struggle to find the right motor oil for my car whenever I’m at the auto store. Apparently the specific type of oil that I purchase is one of the most commonly used motor oil varieties that are sold to the public. It’s the common choice for a slew of sedans from multiple competing brands. Because it’s so widely used, it often is out of stock at the store. I usually always bought my auto supplies at the auto stores, but now I’m ordering them off the internet by necessity. The last thing I ever want is to find that I’m low on motor oil when checking the dipstick and not have any oil on hand to top off the engine. I’m afraid of what could happen to my engine if I ran it for too long while it’s low on motor oil. I deal with a similar situation regarding my air conditioner. As much as oil is an essential in cars, air filters are essential for central HVAC systems. My air conditioner wouldn’t have survived nearly as long as it has thus far if I had neglected filter changes. Unfortunately, my filter dimensions are 18 inches by 18 inches, which apparently is an extremely common filter size. I hate going to the store for a new air conditioner filter only to discover that none are in stock. Air filters aren’t as easy to find on the internet as motor oil, so in the end I’m forced to visit several stores until I can find a filter for my air conditioner. I don’t want to go long without a new filter and cause damage to my air conditioner. I’m just going to have to buy HVAC filters in bulk from now on.