Tap Size for M5 Steel Bolts

[oskar]

I'm working mostly with aluminum 3/8" to 1/2" thick and M5 steel bolts are the most I use. My charts indicate the tap size drills for M5 bolts is #19 or 11/64".

The other day I used by mistake a 3/16" drill instead of 11/64" (in my drills holder the 3/16" is next to 11/64" so I picked the wrong one).

Using the tap to make the threads I noticed the tap went thru quite easy so I said perhaps something wrong with the aluminum casting. Then I try to screw a M5 bolt without tapping first and the bolt went in kind of tight but I was able to hold good 2 pcs together without stripping the threads.

Is it acceptable to use 3/16" drill to tap for M5 bolts?

Many thanks

 

[ARC-170]

"Then I try to screw a M5 bolt without tapping first and the bolt went in kind of tight but I was able to hold good 2 pcs together without stripping the threads."

Are you saying you used the screw to tap the thread in the hole?

A 3/16 drill is 0.1875" and an 11/64 is 0.172", a difference of 0.016", or about 0.4mm.

 

[Jim F]

I'm working mostly with aluminum 3/8" to 1/2" thick and M5 steel bolts are the most I use. My charts indicate the tap size drills for M5 bolts is #19 or 11/64".

The other day I used by mistake a 3/16" drill instead of 11/64" (in my drills holder the 3/16" is next to 11/64" so I picked the wrong one).

Using the tap to make the threads I noticed the tap went thru quite easy so I said perhaps something wrong with the aluminum casting. Then I try to screw a M5 bolt without tapping first and the bolt went in kind of tight but I was able to hold good 2 pcs together without stripping the threads.

Is it acceptable to use 3/16" drill to tap for M5 bolts?

Many thanks

M5 tap drill is 4 mm

 

[Larry$]

If you frequently use metric fasteners, get a set of metric drills. No need to look anything up. Tap drill size = nominal-thread pitch. 5mm- 0.8mm=4.2mm tap size. #19 drill bit is close.

 

[RaisedByWolves]

I'm working mostly with aluminum 3/8" to 1/2" thick and M5 steel bolts are the most I use. My charts indicate the tap size drills for M5 bolts is #19 or 11/64".

The other day I used by mistake a 3/16" drill instead of 11/64" (in my drills holder the 3/16" is next to 11/64" so I picked the wrong one).

Using the tap to make the threads I noticed the tap went thru quite easy so I said perhaps something wrong with the aluminum casting. Then I try to screw a M5 bolt without tapping first and the bolt went in kind of tight but I was able to hold good 2 pcs together without stripping the threads.

Is it acceptable to use 3/16" drill to tap for M5 bolts?

Many thanks

Boy, where to begin...

None of the sizes you listed are what I would call optimal, and dealing with cast aluminum is tricky even with the correct size taps.

If this were a job where safety was a concern I would want the correct tap, 4mm-4.2mm depending on pitch as mentioned, and would want everything square and proper when tapping.

If this were for say a display item, you would probably be fine, for something structural or any weight bearing item, best hedge towards the safe side and use industry standards.

For aluminum, especially cast I would want 2x the thread diameter of thread engagement. So for a 5mm bolt I would want 10mm or better of thread engagement.

 

[Batmanacw]

4mm is 0.157"
5/32 is 0.156"

I don't have my tap chart with my in my hotel room but I'd make sure you have the correct drill choice.

Little machine shop gives 4.20 mm for m5x0.8 threads. 0.165" for 75% in aluminum.

 

[Ischgl99]

For an M5x0.80, a 3/16th hole will give you 25% thread engagement, not even close to acceptable. #19 is appropriate for 75% thread engagement, and 11/64th would be for 60%. For aluminum, 75% thread engagement is what you should be doing if this needs strength.

 

[oskar]

Yes Jeff, I used the screw to tap the hole.

My experience is with Imperial units, metric system only gives me headaches, lol however I agree its a good idea to get a metric set of drills, like it or not.

Many thanks to all

 

[Ischgl99]

Yes Jeff, I used the screw to tap the hole.

My experience is with Imperial units, metric system only gives me headaches, lol however I agree its a good idea to get a metric set of drills, like it or not.

Many thanks to all

I use metric 95% of the time in my projects, number and letter size drills will fill in the gaps of your fractional inch drills for most metric tap and clearance holes. I only have a few metric drills in 1mm increments and haven’t found I need more for the majority of my uses.

 

[Larry$]

metric system only gives me headaches

I grew up imperial system. I started using metric in my work. It is now my preferred system. Units of ten in everything. Lineal & volumetric easily converted. Threading: nominal size minus the pitch gives tap drill size. Learn to think in it instead of trying to convert. 50 years ago this country almost went metric. Stupid politicians stopped it. The origin of the 2 liter plastic Coke bottles.