# Understanding hole specifications

I am trying to interpret the hole specifications in the attached diagram. What does each component mean? I understand what 'Thru All' means, does 4x mean 4 holes? What is the diameter of the hole? is it 5mm or M6 = 6mm? What is 6H?

4 x means it applies to the four instances that look similar on the drawing.

Ø 5 means the hole diameter (drill size) is 5mm.

“Thru all” is added here to remove the requirement for a section view to show hole depth. You can’t tell by the outlines whether it’s through, or you can see the bottom of the hole

M6x1.0 - 6H is the thread and tolerance to be tapped into the drilled hole - again, through all. With blind holes it’s often the case that a minimum thread depth is specified that’s less than the hole depth to avoid multiple tapping operations using a bottoming tap.

This drawing would likely be better using a centreline and symmetry to dimension the hole positions. Even if distances to the bottom right corner are critical, it still needs some sort of ‘construction lines’ to e.g. show that the top left hole is at the same vertical height as the top right. This is a fairly simple part, but in more complex geometry you can’t assume things like that unless they are explicitly shown. Adding centrelines would do this.

• Thank you for the very clear explanation, so what I understand is that a 5mm hole is drilled in the part as a pilot hole, it is then tapped with a M6 thread. Am i right? And if I have to select a screw for this hole it has to be a M6 screw? Commented Aug 19, 2018 at 15:22
• You could change the bolt to a similar diameter one in UNC, UNF or whitworth but the expalnation is clear... Commented Aug 19, 2018 at 15:26
• I would dispute that you need "construction lines" to show the positions here. First, the fact that they are called out as "4X" means they are all in the same position relative to other features. Second, you never use construction lines or dimensions for things that are "obvious" from the drawing itself, like showing that the corners of the quadrilateral plate are all 90 degree angles! Commented Aug 19, 2018 at 17:40
• This drawing would certainly still benefit from centrelines, being symmetrical. If the outer profile were not a straight rectangle it wouldn’t be clear that the holes are horizontally consistent, and the 4x only covers diameter and depth etc, saying nothing of position. In this particular drawing it’s not misleading, but I was trying to squeeze in some general ‘best practice’ suggestions into my answer! Commented Aug 19, 2018 at 18:12