A bit narrow as acid brushes go but a handy width for lapstrake planking gluelines.

I've been using these acid brushes for something like 45 years now. I started using them as an aircraft machanic first and because they are so easy to use have used them on cars and boats as well. They are basically throw-away brushes except for grease, where I keep one for years with the container. Also, in hard to get to places, they bend pretty easy to a 45deg, and even to 90deg's and still do the job.

I bought the twelve dozen box. I use them for applying grease, glue, cleaning solvents, etc. Use them once and toss. Very economical. Keep a bunch in your shop.