Breadboards - distance between power busses

 I am making some utility boards for breadboard power supplies and i/o. 

This means I have to know the exact dimensions of the breadboards. 

The senter piece is easy - holes are about 0.1" apart (though measuring the exact dims it seems that they are often a little off, just not enough to be a problem). In addition there are two holes missing in the middle. Distance between the two outer holes is then 1.1" or 27.94mm.

By looking at the cards I expected the same to be true for the distance between the columns and the horizontal "busses", after all, this would seem the reasonable thing to do. But this turned out to be a mistake! 

I did some googling, and found a site that showed a board that had the distance between the outer busses as 1.85" (the expected would be 1.9 if all holes were 2.54" apart).

I then made my cards to this standard, but when doing a test print, this turned out to be too little... The busses on MY breadboards at least are further apart. To make things worse, there are differences between cards that look similar but are from different vendors/orders ("luckily" there is also differences in the spacing of the tabs that connects the cards so cards from different batches cannot be connected properly - making it easy for me to know what cards are from what batch).

So, I have to take some accurate measurements to figure out what is going on.

Here are the dimensions of my two batches of boards:

A: Power busses: 9.40mm, main part: 35.45mm, total w/gaps: 54.58mm

- gaps are 0.17mm

- padding around busses is 3.43mm per side

- padding on main part is 3.76mm per side

- calculated distance between outer bus lanes is 47.74mm = 1.879 inches

B: Power busses: 9.45mm, main part: 35.5mm, total w/gaps:54.64mm

- gaps are 0.12mm

- padding around busses is 3.46mm per side

- padding on main part is 3.78mm per side

- calculated distance between outer bus lanes is 47.74mm = 1.879 inches

Wow, that was a bit surprising. Even though things looked very different, the inaccuracies evened out to make the end result equal for both batches. With the pretty lose tolerances in the making of these cards, I'd say that 1.88 inches is probably the distance to aim for. Measuring using digital callipers give a very similar result for both cards. 

As for the bus distances between cards with two and tree busses between them, they should be:

2 busses (four lanes) - distance between outermost lanes of each card: 

A: 2 * 3.43mm + 0.17mm = 7.03mm

B: 2 * 3.46mm + 0.12mm = 7.04mm

0.275 inches is 6.99mm, which is a good approximation

3 busses (six lanes) - distance between outermost lanes of each card:

A: 2*3.43mm + 0.17mm + 9.40mm = 16.43mm

A: 2*3.46mm + 0.12mm + 9.45mm = 16.49mm

0.65 inches is 16.51mm, which is a good approximation