Proper size hex bits with small Allen ends?

[JHZR2]

I need to replace a gasket on a diesel injection pump, and the only practical way to get the screws out is to loosen them with a 1/4” hex Allen bit in the right head size for the screw. Bits like this:

For a location like this:

I think it takes a 4mm Allen. A 4.5 or 5mm won’t fit. But a 4mm is loose. I appreciate how important it is to have a tight fit full depth of the Allen into the female end. So my 4mm is no good. I could crack a screw when I tried but one rounded out would be a major issue. It only takes one.

I tried a 5/32, and it fit better. This is a Bosch diesel pump. I doubt the OE screws are imperial. Keep in mind the only bits of this kind I have are from some multi bit sets that were gifted to me long ago.

And, 5/32 = 3.97mm. Yet it fits tighter.

I checked the measurements. The 5/32 is slightly bigger than the 4mm but not really so unless you are looking at tiny fractions of an inch on a dial caliper.

Marginal differences.

So, who makes quality, proper fitting bits of this kind that I can count on?

Any recommendations?

Thanks!

 

[wings&wheels]

My go-to for quality bits, etc.; Wiha

 

[atikovi]

I think it takes a 4mm Allen. A 4.5 or 5mm won’t fit. But a 4mm is loose.

If 4mm is loose it's probably 5mm that is rust jacked or has dirt in it. Clean it out with a pick and try again. Never heard of 4.5mm.

 

[RooflessVW]

Wiha unless you want sockets. Then Snap-On. Nothing else is worth spending time on

 

[MSCH]

Marginal differences.

So, who makes quality, proper fitting bits of this kind that I can count on?

Any recommendations?

Thanks!

have you tried putting a piece of tape on the end of the hex bit and tapping it into the fastener hole? I don't think you are going to find a tool that fits perfectly unless it is some proprietary tool of esoteric manufacture. By the photos it looks like you don't have alot of room to get in there, is it possible to remove the stuff in the way so you can get a straight shot at it and get a small impact driver in there and tap it with a hammer?

 

[64bawagon]

Cleaning the internal hex is the most important part of this. I agree that its unlikely that the screws are fractional.
A 4.5mm hex is a real possibility. You might try a good long arm hex key assortment that has a 4.5 and test the sizing after the cleaning.
Is there a chance you could confirm the size with a repair manual for that pump ?

 

[B6_Dolphin]

So, who makes quality, proper fitting bits of this kind that I can count on?

Any recommendations?

Thanks!

I recently purchased these impact bits off Amazon to work on my Ducati. So far they are holding up well...

https://www.amazon.com/dp/B01LXB41CR?ref=ppx_yo2ov_dt_b_product_details&th=1

 

[Chris142]

For something that needs to be perfect or it can cause a major problem I would get a snap on made one. I'd even buy the 4 mm and 5/32 and use whatever fits best.

 

[SunnynHollister]

My go to for something like this is my trusty Chapman set. Made in US and has never failed me. I've been using them for work and home for over 20 years:

#5575 Master Screwdriver Set | Chapman MFG

5575 is Chapman’s most complete precision screwdriver set total 56 pieces with 51 insert bits which include Slotted bits, Phillips bits, Metric and SAE Hex Bits, and Star bits which fit Torx screws. Over 300 tool combinations! Machined from USA steel with a black oxide rust inhibitor finish...

chapmanmfg.com

 

[vavavroom]

Never heard of 4.5mm.

The small metric hex sizes are interesting: 0.70, 0.71, 0.89, 0,90, 1.00, 1.20, 1.27, 1.3, 1.5, 2.0, 2.5, 3.0

I'd machine/file and sand a too-large hex bit so it will fit tightly or I'd use a ball hex that can be canted to sufficiently grab the hex bolt, then replace the bolt.

 

[JHZR2]

Cleaning the internal hex is the most important part of this. I agree that its unlikely that the screws are fractional.
A 4.5mm hex is a real possibility. You might try a good long arm hex key assortment that has a 4.5 and test the sizing after the cleaning.
Is there a chance you could confirm the size with a repair manual for that pump ?

I tried a 4.5 craftsman L type and it is definitely way too big.

 

[drtyler]

I might try this

Snap-on Store

shop.snapon.com

Or this

Snap-on Store

shop.snapon.com

Their coated bits typically do not fit loose.

There is a Hazet 4mm with 1/4” drive that is coated, but you may not have enough room.

Hazet 8501-4 4mm Hex Titanium-Nitride 1/4" Socket

Hazet 8501-4 4mm Hex Titanium-Nitride 1/4" Socket - high quality German engineering at the lowest price. Free same day shipping available.

www.kctool.com

Sanding and filing on the 4.5 you have might be the option to get it done today.

 

[Trav]

Are you sure they are not Torx?

 

[Fla]

I need to replace a gasket on a diesel injection pump, and the only practical way to get the screws out is to loosen them with a 1/4” hex Allen bit in the right head size for the screw. Bits like this:

View attachment 152247

For a location like this:

View attachment 152248

I think it takes a 4mm Allen. A 4.5 or 5mm won’t fit. But a 4mm is loose. I appreciate how important it is to have a tight fit full depth of the Allen into the female end. So my 4mm is no good. I could crack a screw when I tried but one rounded out would be a major issue. It only takes one.

I tried a 5/32, and it fit better. This is a Bosch diesel pump. I doubt the OE screws are imperial. Keep in mind the only bits of this kind I have are from some multi bit sets that were gifted to me long ago.

And, 5/32 = 3.97mm. Yet it fits tighter.

I checked the measurements. The 5/32 is slightly bigger than the 4mm but not really so unless you are looking at tiny fractions of an inch on a dial caliper.

View attachment 152252View attachment 152253

Marginal differences.

So, who makes quality, proper fitting bits of this kind that I can count on?

Any recommendations?

Thanks!

Try several different bits. Even within the same brand, they do vary slightly in size. A few years ago I had to open a printer that used Torx bits and I had trouble fining one that fit. I ended up carrying the printer into the local hardware store and trying out all of their Torx drivers until I found one that fit securely. I keep a lot of extra sockets, wrenches, etc in my tool box because you always find certain fasteners that are too large or too small to fit a one correct size tool but other tools will fit them.

 

[Trav]

My money is on a T20 = 3.97mm

 

[D60]

If you want a 4mm that can theoretically "grow":

3/8 Inch Drive Worn/Damaged Hex Bolt Extractor Socket Set 5 Pc | Astro Pneumatic

Astro Pneumatic 1047 5 Piece 3/8 Drive Worn Damaged Hex Bolt Extractor Socket Set Automotive auto hand tools

www.toolsource.com

But yeah, I'm embarrassed to say that on at least a couple occasions I've tried to use hex when it's Torx. It can be difficult to tell/see with the smaller sizes

 

[SubLGT]

Wera Hex-Plus bits?

Hex-Plus

Hex socket screws with rounded out heads are not uncommon. Working on these screws is usually difficult and frustrating. We took a close look at the hexagon form and improved it. Screwdrivers with Hex-Plus have a larger contact surface, and prevent the destruction of the screw head, providing up...

www-de.wera.de

Wera 056684 Hex-Plus 4 x 25mm Insert Bit

Wera 056684 Hex-Plus 4 x 25mm Insert Bit - best deals on German tools and high quality engineering. Free same day shipping available.

www.kctool.com

 

[JHZR2]

My money is on a T20 = 3.97mm

Actually, with a little more looking and cleaning, I realized they were T30!!

So much for Allen dimensions being the issue.

Now I need to figure out how to get upward force into a t30, coming at it from the top, so I can crack these screws.

It’s for the lower cover of a Bosch injection pump, on the bottom of the IP.

 

[TheLastWord]

Actually, with a little more looking and cleaning, I realized they were T30!!

So much for Allen dimensions being the issue.

Now I need to figure out how to get upward force into a t30, coming at it from the top, so I can crack these screws.

It’s for the lower cover of a Bosch injection pump, on the bottom of the IP.

View attachment 152335

T30 is 3/8" .375" 5.2mm Not even close to your initial posts.

Are we talking about about a different location of the fastener?

Or excessive crud, corruption, rust, grease, etc?

 

[Trav]

Actually, with a little more looking and cleaning, I realized they were T30!!

So much for Allen dimensions being the issue.

Now I need to figure out how to get upward force into a t30, coming at it from the top, so I can crack these screws.

It’s for the lower cover of a Bosch injection pump, on the bottom of the IP.

View attachment 152335

I sure looks like a hex in the picture but a torx will take it out if you can get on it. That is going to be a real bugger, the pump usually gets pulled for something in that area but that is something you do not reaally need to get into. How bad is the leak?