M4 Mounting hole dimensions - Page 1
Forum section: electronics / general

author: jtronix
author_rank: Regular Contributor
timestamp: August 11, 2018, 07:02:01 am
content: I just got table where all dimension is mention till M3.5 but i need M4 dimensions.I know Hole size required for M4 screw4.152 - For Tight fit4.445 - For Loose fitCan anyone know how to to calculate Top Pad size?

author: saike
author_rank: Regular Contributor
timestamp: August 11, 2018, 08:16:59 am
content: I just measured a 4mm pan head screw on my bench here. The head diameter is 7.8mm and the flat washer for it is 9.8mm diameter. It is probably a good idea to get one and measure it yourself, the washer sizes vary a lot.

author: jtronix
author_rank: Regular Contributor
timestamp: August 11, 2018, 10:15:11 am
content: I need dimension for create footprint for my PCB.see attached image which all i needNote that vias on pad are optional.mainly i need calculation of D (pad size) like in my first post top pad size is given in chart

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 11, 2018, 07:39:24 pm
content: Pad size depends on fastener head size and if washers are used, their size as well.We can't answer any more accurately than this. However, you can peruse catalogs likewww.mcmaster.comand find drawings and dimensions for everything under the sun.Tim

author: Siwastaja
author_rank: Super Contributor
timestamp: August 13, 2018, 09:20:31 am
content: This is not something you can base on a generic table, so please recheck your hole size assumption.Any M4 screw will always fit into a 4.0mm hole, 100% guaranteed.So everything you need to do is to guarantee your hole always is at least 4.0mm in size. If you have multiple mounting holes, you need to add worst case dimensional instability and worst case offset error between the holes, so that if one of the holes is slightly at the wrong place, the screws will still fit. Since the PCB manufacturing tolerance, and FR4 stability tends to be very good, the mechanical side dominates: how repeatable are the mounting posts or holes in the case? You'll get this tolerance from the manufacturer of the case, and it will directly determine your hole size - no one can put it in a generic table.For example, if the case holes are hand-drilled using a template, expect +/-1mm error, necessitating 6mm hole size! If they are hand drilled using a precision jig, the error would be maybe +/- 0.5mm max. If CNC laser cut using modern machinery, then you won't need to worry too much.For pad size, look at theactualscrew you are going to use, and simply look at its drawings; maximum head dimension.If you don't know the exact screw type you are going to use, or won't have a proper datasheet (i.e., use "generic" hardware store stuff, or Ebay stuff), look up for a fewsimilar lookingscrews with proper datasheets, use the biggest value you can find, plus add a bit margin.

author: madires
author_rank: Super Contributor
timestamp: August 13, 2018, 10:38:06 am
content: Quote from: Siwastaja on August 13, 2018, 09:20:31 amCould be a tight fit. Usually 4.2mm work fine.

author: mathsquid
author_rank: Frequent Contributor
timestamp: August 13, 2018, 10:13:50 pm
content: Little Machine Shop has a PDF that gives clearance and tap drill sizes for all the standard small sizes.https://littlemachineshop.com/images/gallery/PDF/TapDrillSizes.pdf