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Plug Tap.... Engineering


Mutley

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I am after a few Plug Taps to clean out various bolt holes when working on the Defender, as they are often cacked up with locktite and the likes...

I dont want a Tap and Die set, just the plug tap in 11mm, 13mm, 15mm and possibly 17mm..... Could some kind knowledgeable type tell what to ask/look for ie are they called M11 taps as for an M11 bolt hole and M13 tap for an M13 bolt hole and so on? Also what pitch do i need to be getting them in???

And most of all where to get them from? Because if it is the case M13 tap for an M13 bolt hole, most places on the web only seem to do even numbers after M10???

Cheers Andy 

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While I’m sure they exist, those are not common metric thread sizes. I’m not aware of any non-standard threads being used on Defenders in any great quantity - the odd thing here and there.

A tap and die set is a very useful thing to have in the tool collection.

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If all you want to do is clean threads out, then don't worry whether they're plug, second or taper taps - just buy whatever ones come your way (like at an autojumble or car boot sale) and simply grind the ends off.

Depending on what Land Rover you have, you'll need them in at least 5 mm, 6 mm, 8 mm, 10 mm. and 12 mm They go a lot bigger in certain places, but those are the most common sizes.

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Thanks guys.....

So if lets say the bolt head requires a 13mm spanner, how do i know which tap to use, as obviously i don't want to cut it bigger, just clean the thread out?....

Is there a conversion system/method for this?

Thanks again

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Bolt head sizes can vary for any given bolt thread size/spec.

There is no direct conversion, you need to measure it.

I get the feeling you are overthinking things, buy a tap/die set and get used to using it, they are invaluable.

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Measure the diameter of the bolt shank. If the diameter of the shank is 8 mm then the threads are M8. Never mind the bolt head, an M8 bolt can have a 13 mm hexagon if it is manufactured according to DIN, a 12 mm bolthead is in accordance to ISO, on newer types you may find an M8 flange head bolt for a  10 mm spanner while an M8 socket head bolt requires a 6 mm Allen key. And these are all standard bolts, nothing special. Measures the bolt shank, the only way to make sure what thread it is.

Thread pitch is regularly 0.8 for M5; 1.0 for M6; 1.25 for M8; 1.5 for M10 and 1.75 for M12.

Drill size is nominal thread diameter minus pitch. So for M6 drill 5 mm( 6-1.0=5). For M10 drill 8.5 (10-1.5=8.5). This rule works for finer pitched threads too. For instance if you ever have to tap an M10x1.0 thread your drill size needs to be 9. It really is that easy.

Edited by AV8R
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Size of the head is absolutely meaningless you need to measure the thread size.

also bear in mind that not all the threads on a landrover are metric, there is mix of metric, UNC, UNF, And BSF at the very least.....

get yourself a vernier, a set of thread pitch gauges, and a Zeus book, as the only way to identify a thread size is to carefully measure it!

 

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I learned the hard way about this and used to buy things one at a time. Now I know that having a set means I'll be ready for the next time - and if you do your own work, there will be a next time! 

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http://www.tapdie.com  are the dudes for ANY type of tap, die, or weird drill bit.

Cromwell do a lovely set of taps + drills for the workshop. Has the drill bit and 3 taps per size (starter, second, bottom) and is much nicer quality than the usual cheapy kits.

Also Chronos and RDGTools are sources for half-decent bits like that, as well as the thread gauges.

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Most of what I was going to write has been said above about the sizing of the threads. 

For what you're doing a cheapy set would be fine for clearing out threads, but if they're going to be used for cutting new I'd buy a branded set, or single sets of decent ones.

If you're replacing the bolts on what you're doing, you can sometimes clear up threads with the old bolt if you cut a slot down the side of it with a 1mm cutting disk). It gives a sharper edge to scrape the threads on the way through and remove any loctite etc. Not as good as an actual tap but can be good enough sometimes.

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If you can get a bolt to fit the hole take the bolt to a tool shop or bolt supplier, Cromwell or bapp or whoever is local to you, they will be able to tell you what it is. I don't know exactly what vehicle you've got but do you know it's metric?

There are also thread  repair / cleaning tools which look like a file and have a few different pitches on so you can chase out the dirt.

I do find this a very useful book to have in the garage for the price https://www.cromwell.co.uk/shop/cutting-tools/reference-and-data-books/the-ref-flipcharts-5th-edition-wiro/p/CAT8492621A

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2 hours ago, landroversforever said:

Brain fart there as they are available, you just never see them being used. They are carp  :lol:

Depending on your business, I think. Actually I used them last week to save some threads with worn /abused beginings. Parts were good to go after some strokes with the file. You do need to select the correct pitch and file at an angle to parallel the original thread properly. Being a tool maker in a large aerospace  factory, I do need to restore some threads now and then.

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