The julep strainer is designed exclusively to filter out large chunks of ice. It's a concave piece of metal with equally sized holes throughout. This allows liquid to flow through while restraining any large chunks of ice. They are designed specifically to fit the standard mixing or Boston glass. Tere is some debate as to how the julep strainer best meshes with the glass. Most people insert it with the bowl facing up as this tends to allow a slightly firmer grip on the handle butIt does allow very small chips of ice to flow through, but these melt almost immediately. The ideal time to use a julep strainer is when you are making a stirred cocktail. They are ideal for drinks that are made solely from spirits, like martinis. Julep strainers do not function very well at filtering out juice pulp or other particulates.
A Hawthorne strainer is probably the strainer that bartenders are most familiar with. Most are comprised of a flat piece of metal with holes and a handle. What makes it a Hawthorne strainer is the spring running around the edge of the bottom of the strainer. This enables the strainer to be adjustable and fit a variety of pouring vessels such as a mixing glass or beaker, a mixing tin, and a cheater tin. The spring also allows the strainer to be adjusted while sitting in the glass or tin. You can pull the strainer back to allow pulpy juices to flow through. You can also press it forward to force the liquid to flow through the spring and the flat metal piece filtering out much more dense pulp. Pretty much whenever you make a shaken cocktail, a Hawthorne strainer is the best strainer for the job.
“Alcohol lowered inhibitions. It didn't create impulses that weren't there.”
- Chelsea Scott