Drawing the land pattern for a through hole part and am seeing this extra information below the main hole diameter (and tolerance):

through-hole PLC spec

For example, let's look at the one drawn right below the LED symbol (this is for a RJ45 connector with embedded status LEDs). I see the main part is diameter 0.89mm but...

  1. What is the 0.035mm beneath it?
  2. What does PLC stand for? It's not the first time that one has showed up on these datasheets, but I cannot for the life of me find the meaning of this acronym. I noticed the diameter was quite small, so wondering if this is a pilot hole location. My guess was "pilot location center" but that turned up nothing in Google either.
  3. What are the numbers beneath that, in the box, with the ZYX?

Have always had PCB components fit my landing pads, so curious what the engineer was trying to communicate with all this seemingly extraneous info.

Note: It is unfortunate that the word PLC means something else regarding electronics. That has made searching for this on stackexchange or elsewhere practically impossible with all the noise.

Thanks for the future edification!

  • \$\begingroup\$ Why do you think that the measurement is in mm? \$\endgroup\$ Commented Oct 6, 2015 at 19:49
  • 1
    \$\begingroup\$ The numbers in square brackets are inches. "PLC" means "places", so there are four .035" holes, and two .062" holes in the pattern. \$\endgroup\$ Commented Oct 6, 2015 at 19:55
  • \$\begingroup\$ The [bracketed] measurements are the imperial equivalents. The boxed measurements are the unplated raw drill size (mm and [imperial]). \$\endgroup\$
    – user16324
    Commented Oct 6, 2015 at 19:55
  • \$\begingroup\$ IIRC, the XYZ are datums used for referencing where the dimensions are measured with respect to. \$\endgroup\$ Commented Oct 6, 2015 at 19:57
  • \$\begingroup\$ Oh, duh. Everywhere else they are in [ ] it is imperial, so I don't know why I got thrown off with the holes specifically. Perhaps thinking PLC meant something pilot or plated related. Must need more coffee today... Thanks \$\endgroup\$ Commented Oct 6, 2015 at 20:05

1 Answer 1


0.89mm = 0.035 inches. 4 PLC means in 4 places, that is, there are 4 such holes. The box around the 3.43 dimension indicates that this is a basic dimension, that is, the ideal position of the hole. The Z, Y, and X are the primary, secondary and tertiary datums that the basic dimensions are referenced to. The cross-hairs looking symbol in the box below the hole dimension means this is a position tolerance for the location of the hole. The center of the actual hole has to lie within a 0.1mm circle that is located at the "true" position. The M in the circle means that the position tolerance is for the hole at "maximum material condition" which for a hole means it is on the small side of the allowable diameter (0.81mm in this case). If the actual hole is bigger, then that much extra is allowed on the position tolerance.


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