Eventually during your DIY journey you will encounter a situation where you will need to use a razorblade. Maybe you will need to scrap something of a granite counter, scrap something off glass, or some other situation. The thing is holding a razor blade with your hand is a risky proposition, as it is very easy to accidentally cut yourself.
This is where a razor blade holder comes in. The razor blade holder lets you secure the razor blade, allowing you to use the razor blade while minimizing the risk of accidentally poking or cutting yourself. Also, often they come with a cover, further reducing the risk on an accidental cut. Lastly they are relatively inexpensive, usually $5-$10.
A good razor blade holder can be found here on Amazon here:
Titan Tools 12031 4-Inch Mini Razor Scraper | Includes 1 Extra Heavy-Duty Razor Blade
These razor blade holders have a lot of uses. One of the best uses is scraping things stuck on glass (things caked on your windshield or even your shower door). Also, you can use them to scrap of paint or other uses, basically anything where you need a thin but stiff edge.
In the following video I talk more about the razor blade holder and show how to use a razor blade to remove hardened soap scum on a shower door.