Odd pin block

[jimialeggio5 at comcast.net]

Ron wrote:
 
"I use 1/4" for the first pass, and 6.8mm for the second for 
2/0 pins."

Ron,

When I double drill, since accuracy is the point,
it's hard to center the second pass on the first hole unless 
I switch bits before moving on to the next hole...a real pain.

I assume you don't change bits for each hole, right?  If you come back to all the 
1/4" holes for the second pass,how do you spot the center.

Jim I