Most bench dog holes are 3/4" but to buy the dogs commercially can be somewhat expensive depending on what you purchase. I decided to make my own on the cheap and here is what I came up with. I had these materials in my shop but to purchase them would be very inexpensive. For example, most auto parts stores sell the heater hose by the foot and unless you want to make a lot of these you will only have to buy one foot.
Step 1: Materials
I had some 3/4" emt tubing (electrical conduit) in my shop and decided to try and make something with this, the diameter was perfect but there was nothing to hold them in place. Any 3/4" O.D. tubing would work, just don't use aluminum as it will crush.
Step 2: Hosed
I thought of automotive heater hose as it is available in different inside diameters, a common one being 3/4" which is the same as the O.D. of the emt tubing.
Step 3: Assembly
I cut the emt and the heater hose to appropriate lengths and with a shot of WD-40 on each assembled the bench dogs in a few minutes. Definitely not pro level bench dogs but very effective. I have an old model Black & Decker workmate for which I made up two new wooden top pieces (the old ones were toast) and these bench dogs work perfectly for holding all types of work. I'm also going to make a set that only protrude from the top 1/4" or so to hold thinner stock for planing and the like.