Doesn't quite work like that. It is dependant upon the manufacturer and the
drill size. On average it is about 10% of the drill size rounded with a minimum tolerance.
Conventional (everyone)
.010" - .003"
.030" -  .004"
.050" - .005"
Advanced (roughly 9%, min .002")
.010" - .002"
.040" - .003"
.050" - .004"
You will find variations and some that can do even better, but this is my rule of thumb.
It is a percentage, similar to the aspect ratio of board thickness to minimum drill size.
(not a guru though)
Chris Robertson
Author "PCB Designer's Reference"
[log in to unmask]
ISBN: 0130674818
Search for it at www.amazon.com


  ----- Original Message -----
  From: Tom Burek
  To: [log in to unmask]
  Sent: Monday, December 15, 2003 2:36 PM
  Subject: [TN] Hole tolerance


  Greetings guru's,
  I have an inquiry into hole location tolerance, especially directed to our
  many PCB manufacturers listening in.

  What is the best reasonable tolerance you can expect, world wide,
  (overseas as well as domestic suppliers), for positional location of
  plated and unplated holes, without adding addition cost to the circuit
  board?

  Expressed in a true position format, would a diameter of 3 mils. be
  unreasonable?  dia. .005?

  Assume a moderate volume of production.

  Thank you in advance.

  Tom Burek
  Ametek/Dixson

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