One of the great things about Safety Razors is the choice that you have. Especially with 3-Piece Safety Razors, as the head is a seperate piece and can be easily swapped.
Here are the different Head Types you can choose from. Most of the names given to these heads refer to the safety bar. This is the horizontal bar on the bottom plate that runs underneath the actual blade. It is the most important piece of the head, providing you with the protection from the blade, hence the name "safety bar". Changes in the shape of this bar will give different shaving experiences.
Common name given to heads that have a simple straight safety bar that is flat. This is often found on vintage razors and they tend to offer a very safe mild shave. The flat bar minimises the amount of hair exposed to the blade, so you will normally need more passes to get a close shave.
Scalloped Safety Bar
This style has become the most popular, or most common, shave head type. Similar in every way to the "Safety Bar" except the bar is not flat, it has regular undulations that allow more hair to be exposed to the blade. This head provides a great all round shave and has become a favourite for those with sensitive skin.
Cobbled Safety Bar
These heads are similar to the "Scalloped Safety Bar" Heads but instead of the smooth undulations the gaps are more squared. AKA as Closed Comb. These gaps act more like a guide, steering the hair towards the blade and maximising the amount of hair cut with each pass. The "Cobbled Safety Bar" Heads are considered middle of the road aggressiveness.
The "Open Comb" head goes one step further from the "Cobbled Safety Bar" and opens up spaced channels for your hair to pass to the blade, usually considered the more aggressive type of head but can also provide a very "efficient" shave.
Double Open Comb
Same as above for the bottom plate, however in this instance the top plate of the head is also of an "open comb" type. This top plate style is great for capturing slick shaving soap and giving you a slightly increased buffer between the razor & skin. AKA "Self Lubricating Razor"
The Slant head is a simple concept that many swear by, the "twisted" head holds the blade at an angle that creates a "slicing" motion across your beard. Very efficient and liked by many with sensitive skin. It does require patience and technique.
Single Edge Head
More of a different style of head than type of head, the Single Edge Head is just one sided and will usually take either a half DE Razor Blade, or an Artist Club Style Blade. They are making a comeback in the market and many people prefer their efficiency and looks.
So now you have a better understanding of the terms used you will notice that sometimes a single term isn't enough to describe a razor head. Good case is above Slant Head by YAQI. It is a SLANT head, but it also has a "Scalloped Safety Bar" and a "Open Comb" Top Plate.