Bond beam units described by concretemasonry...where slots are cut at jobsite are shown in Fig 2. The slots can also be made at the plant..and is done after units have been fired.
The coring size will differ depending on the manf., but the cores serve 2 purposes. First is it allows even firing on the clay mass. The face shell (distance from the edge of the core to the face of the brick) is about 3/4". The distance between each core will be roughly about 3/4" (that dimension will differ depending on the manf.) Having a balanced clay mass evens out the temp. of the brick during firing and avoids a "banana" configuration that results in uneven firing.
The 2nd reason is it reduces the weight of the unit, taking less clay to make and saving costs (and less cost to ship).
The 3/4" dia. cored hole is too small for reinf, that's why there is "clay block" as I call it...or Hollow Clay Masonry. There are a few plants in North America that make these types of units...Interstate Brick (Utah), Mutual Materials (Washington state), Summit Brick (Colorado), Carolina Brick (North Carolina) and a Canadian company called IXL.
There were questions on Hollow Clay brick and the use of bond beams. I was Interstate Brick's Tech Manager and the only way a bond beam could be created was by the mason...where he rips along the length of the brick (flush to each inside face of the face shell and the upper half of the unit's height). This creates a tab that can be popped out with the tap of a hammer.
If a kerf were to be cut into the brick before firing, it would cause the unit to crack up. The clay mass needs to stay as balanced as possible (as rectangular as possible) for the unit not to crack up or turn into a "banana". The other reason why this can't be done is the manner of the extrusion process. Its much like a tube of toothpaste...where the brick comes extruded out in 8ft slugs. You can blade or kerf anything in that slug as long as it is continuous and to the slug (visulaize a tube of toothpaste and as you extrude it out, sticking a knife blade to it to create a cont. slot...the same holds true with brick manf.).
After the slug is cut, it goes onto a belt table and where wire blades (like a cheese cutter) cut it into the individual unit sizes. It is only at this step that a bond beam could only be cut or created and the orientation is just to impossible for any machine to get to.
With that said, Interstate did develop an open-ended unit that created kerf's during extrusion (and before the unit goes into the kiln) on the end face shell that could be popped out by a mason. This allows for full head joint construction by having an open end face (i.e., the orientation is an "A" shape).
Seems to me that whatever the original reason, and there are a lot of good ones posted here, the holes, whatever the number, also serve to increase the bond and shear force between the brick and mortar by creating small vertical plugs of mortar into the brick.
