Hi Michael (W),
I saw your post last night and tried to visualise the drawing in my head but failed to see how the 1.5 solution worked out. I knew it must be due to the fact that sine 30 Deg is 0.5. As soon as I drew it on paper the explanation was obvious. When I first looked at the question I thought it was related to some difficulty in measuring the distance between the hole centres. I did think of replying by saying the following. – Put the digital calipers into one of the holes in the way you would do to measure it. Press the zero button. Insert the inside measuring fingers between two holes measuring the distance between the outer edge of the holes. This will give the reading between centres due to the way the calipers were zeroed. The PCD is then this reading over cos 30 Deg. (0.866) I did not do so as I thought my suggestion was too obvious. It did not know until I read some of the replies that basic trigonometry was no longer taught in schools.

Les.

Edited By Les Jones 1 on 16/04/2013 09:41:33

Measure diameter of spindle = X

Measure diameter of hole = Y

Measure distance bewteen spindle and inside edge of hole =Z

PCD = X + Y + 2Z

Joey.