Metric Fastener Help

I'm learning more about fasteners and need some help. I have some rusted fastners holding the sill cover in the tailgate area of a 97 xj. The fasteners are part number 3420 1468, round washer head M4.2-1.41x25mm screws. I'm having a hard time finding them in the 25mm length. I can get up to 20mm easily. chryslerpartsdirect wants $2.50 a pop for them in the 25 mm length.

Question is, can I find this advertised in SAE units as well? I'm a little confused about the M4.2 head diameter. too. Is that the actual head diameter, or is that an approximation?

Thanks in advance for any help.

sgtpeeper said:

I'm learning more about fasteners and need some help. I have some rusted fastners holding the sill cover in the tailgate area of a 97 xj. The fasteners are part number 3420 1468, round washer head M4.2-1.41x25mm screws. I'm having a hard time finding them in the 25mm length. I can get up to 20mm easily. chryslerpartsdirect wants $2.50 a pop for them in the 25 mm length.

Question is, can I find this advertised in SAE units as well? I'm a little confused about the M4.2 head diameter. too. Is that the actual head diameter, or is that an approximation?

Thanks in advance for any help.

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OK - that's a weird ISO callout...

First - SAE and ISO thread forms do not intersect - you're going to use one or the other...

Second - if you're reading numbers off of the screw head, that's a "Property Class" (like an SAE "grade") and refers to the strength of the fastener. I can't recall an M4.2 ISO screw, but there is an M4 (M4-.7) and an M4.5 (M4.5-.75,) so you'll want to check that.

Assuming that you can match it to a standard ISO thread form, you shouldn't have any trouble finding replacement screws. Sounds like you'll want either an M4-0.70x25m/m or an M4.5-0.75x25m/m screw, but you'll want to make sure. The OD of the screw should come to just under 4.0m/m (M4) or 4.5m/m (M4.5,) and the "0.70" or "0.75" refers to the distance between similar points on consecutive threads - like the distance between thread "peaks" being .7m/m or .75m/m.

There is also a "fine pitch" for ISO threads - for both M4 and M4.5, it would be 0.50m/m (.5m/m between thread "peaks.")

Here's a listing of both the ISO "standard" and "fine pitch" thread forms, in case you're interested...

http://www.tribology-abc.com/calculators/metric-iso.htm

Once you have a confirmed size, many fastener houses can help you out - I'd start with either MSC Direct, or possibly McMaster-Carr (but MSC will give you a free catalogue as well - and the damn thing is handy!) Also, look up local MRO houses - local sales tax will almost certainly be less than P&P rates (Pack & Post.)

sgtpeeper said:

I'm learning more about fasteners and need some help. I have some rusted fastners holding the sill cover in the tailgate area of a 97 xj. The fasteners are part number 3420 1468, round washer head M4.2-1.41x25mm screws. I'm having a hard time finding them in the 25mm length. I can get up to 20mm easily. chryslerpartsdirect wants $2.50 a pop for them in the 25 mm length.

Click to expand...

That is quite a weird size, how did you determine that you have 4.2 x 1.41? I'm surprised you even found M4.2!

Question is, can I find this advertised in SAE units as well? I'm a little confused about the M4.2 head diameter. too. Is that the actual head diameter, or is that an approximation?

Thanks in advance for any help.

Click to expand...

You will not find SAE equivalent of metric fasteners. You either have SAE or you have metric. They are quite different. (Save for the one or two SAE threads that happen to fit quite nicely into a metric thread and visa versa)

In a metric fastener, the "4" in "M4" or "8" in "M8" designates the nominal diameter of the threads aka major diameter. This is not the diameter of the head which could vary from manufacturer to manufacturer. The actual diameter often falls just under this number like 5-90 said. For example, I have an M12 in my hand and my calipers say that it is 11.88mm.

I always turn to Mcmaster Carr for the stuff I can't find locally. They have a very nice web interface which you can find bolts easily. www.mcmaster.com enter "fasteners" in the search and start clicking away. Unfortunately I did not find any M4.2 or M4.5 which leads me to ask, if you are indeed measuring the thread diameter and not the head, 4.2mm is very close to 0.164" which is the diameter of a #8 screw. Are you sure what you have is metric?

Ok, reading your post again, I noticed that the screw you are talking about might be threading into sheet metal. If this is the case, then you want sheet metal screws. This could be why you are giving us an extremely large (for that small a screw) thread pitch of 1.41mm. I think a #8 x 1" sheet metal screw will work for you. Even if the thread pitch is different that 1.41mm, sheet metal screws you can just thread it in and it'll be fine. You should be able to get these at any old hardware store except it may not have the fancy head that some automotive fasteners have.



On a somewhat unrelated subject, 5-90, why do you put a "/" between the m's in millimeter? Just curious, never seen it that way.

Get some screws that are just a little bit fatter, ram 'em in there, call it a day. :thumbup:

SuperRA said:

On a somewhat unrelated subject, 5-90, why do you put a "/" between the m's in millimeter? Just curious, never seen it that way.

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Dunno. Bad habit I picked up somewhere (probably England) that I just never saw the need to get rid of.

I'll give it up for Lent - right after I quit drinking...:roflmao:

The first thing I'd investigate here is whether the extra length is needed. A lot of fasteners are a little longer than absolutely necessary. Have you tried a 20 mm to see if it goes in well enough?

Hey fellas, thanks for the responses. I got this screw size (M4.2-1.41x25.0) directly from the parts manual for my 97 xj. I thought this was metric because of the M in front. I have not directly measured it myself, I've only gotten the measurments from the parts manual. It's the screw type holding the sill cover to the body, opposite the liftgate. This screw is indeed a sheet metal screw. I've looked at the existing screws and they have a "self-drilling" style tip.

I found this on the fastenal site:

http://www.fastenal.com/web/products/detail.ex?sku=0162740

This looks similar to what I have, but they only list it on their site up to 20 mm.

On the same page of my XJ parts manual, they list the screws holding the liftgate trim panel as .164-18x1.00, which I'm assuming is SAE. Why would they mix types (ie: metric for the sill cover and sae for the trim panel)? Also, in parentheses next to this number it says "not serviced". What does that mean?

Thanks. Like I say, I'm just trying to learn more about fasteners.

sgtpeeper said:

Hey fellas, thanks for the responses. I got this screw size (M4.2-1.41x25.0) directly from the parts manual for my 97 xj. I thought this was metric because of the M in front. I have not directly measured it myself, I've only gotten the measurments from the parts manual. It's the screw type holding the sill cover to the body, opposite the liftgate. This screw is indeed a sheet metal screw. I've looked at the existing screws and they have a "self-drilling" style tip.

I found this on the fastenal site:

http://www.fastenal.com/web/products/detail.ex?sku=0162740

This looks similar to what I have, but they only list it on their site up to 20 mm.

On the same page of my XJ parts manual, they list the screws holding the liftgate trim panel as .164-18x1.00, which I'm assuming is SAE. Why would they mix types (ie: metric for the sill cover and sae for the trim panel)? Also, in parentheses next to this number it says "not serviced". What does that mean?

Thanks. Like I say, I'm just trying to learn more about fasteners.

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AAH, sheet metal? Baah, just get a #8 sheet metal screw. You won't be able to tell the difference.

Maybe for some reason Jeep decided to use a Metric callout for a SAE fastener because that .164 is a #8 size. You might have a little bit hard time finding a head like that though. Try an auto parts store or you may have to use a washer. Alternately if you absolutely want the exact screw you have (#8-18 x 1"), here is the Mcmaster part number 91515A300. Unfortunately you'll have to buy 100 of them tho. LOL

Replacing the fasteners, you will just have newer rusty fasteners unless you coat them with anti-seize. I use anti-seize on essentially all exterior bolts on the XJ- I can actually remove rear shock bolts without breaking them now! This is on a 1990 driven since new on roads with winter salt, and on a 2001. Works for me.

Have you thought about using some rust remover and then repainting them?

Everytime I go to the junklyard I bring home a pocket full of spare and replacement fasteners from the Jeeps.

Larger NAPA stores or an autobody supply house will have small packages of automotive fasteners.

www.allchrysler parts.com is one of the cheapest online parts places.

http://www.nutty.com/ has lots of fasteners and they will gladly deal with small and/or retail orders.

Not Serviced means the part is not individually stocked or issued, it is either part of a repair/replacement kit or is a bulk item the repair tech should have in the tool box.