I can see how significant it is for you to add fractional sizes to your products, David.

Let's take some troubleshooting steps to ensure you can add a slash while using your QuickBooks Online (QBO) account. An accumulation of historical data can cause unexpected behaviors. 

To begin, open your account through an incognito window to rule out the possibility of a webpage issue. You can accomplish this by utilizing the following keyboard shortcuts: 

• Safari: Control + Option + P
• Google Chrome: Press Ctrl + Shift + N
• Firefox or Internet Explorer: Ctrl + Shift + P

If that works fine using a private browser, go back to your original browser and clear its cache so the system can start fresh. Also, using a different supported browser can help us dig deep into the root cause of this unexpected behavior.

However, if you'd like to learn more about grouping products and services, here's a resource you can browse: Group products and services into different categories in QuickBooks Online.

Additionally, you can check out this article for more tips and resources while working with QuickBooks in the future: Help articles, video tutorials, and more.

You can always have me if you have other queries about managing your products. Let me know if you have any other tasks that you'd like me to help you with. It would be my pleasure to lend you a hand again.