Carhartt A18 Knit Cuffed Beanie

What's the difference between the A18 and the "Acrylic Watch Hat"?

They're the same hat—the A18 was previously sold as the Acrylic Watch Hat and has simply been renamed. The style number (A18) is unchanged.

Is this a good hat for the jobsite?

Yes—it was originally designed as a workwear essential and is now worn everywhere from construction sites to campgrounds. The hi-vis Bright Lime and Bright Orange options are useful for visibility on a worksite.