Last year when I was closing up the pool, the sight glass on the sand filter broke off in my hand as I unscrewed it. "No problem", I thought. I went to the pool store to get a replacement, and they didn't have any. I went to another pool store, and they didn't have any either. Neither store could order one -- They didn't have my pool filter type in their system.

I did some online research and discovered that my pool filter was made by a company in Toronto that went out of business many years ago. I talked to another pool store, and they recommended that I just plug the hole where the sight glass attaches and live without it, or replace the entire filter system.

I went home and thought about the problem. If I was making pool filters, and there was one part that had to be made out of glass, surely I would outsource the glass-making part to another company. Furthermore, the cheapest thing to do would be to ask them to make something that their factory can already make. Therefore, the threading for the sight glass must be a standard threading, and the size must be fairly standard as well.

So a new online hunt began: For companies that make glass jars. First, I researched standard bottle neck finishes and used a measuring tape to try to figure out what threading size I needed. I guessed that a bottle with a 24-400 thread finish would be about right. With these types of jars, you usually have to order them by the case, so I ordered some from Amazon to try. They were too small, but I was able to return them.

Based on that, I guessed that I needed a 28-400 thread finish. This time, I had to order a pack of 36. And it worked!

When you consider the normal cost of pool parts, $45 for a new sight glass is not unreasonable, and I now have 36 of them! By the way, if any of you know anyone with an obsolete pool filter and a broken sight glass, send them to my eBay auction, where they can get a replacement for the completely reasonable price of $30! If I sell even two of the extra 35 that I have, I will be ahead!

Technical Details: These photos were taken with my Pixel 6.