Metric grease fittings

[Snagglefoot]

Looks like I busted a right angle grease fitting
on an AC Delco lower ball joint. To unscrew the fitting from the ball joint I had to use a 10 mm wrench. A 3/8” wrench was too small. Does this mean the thread is going to be metric? I have a English sized grease fitting to take its place and the threads seem to mesh but hard to tell. There is not much room to start the threads on a new grease fitting so I was thinking I should get a M6 to check it out. Any opinions out there? Thanks.

 

[Trav]

If it is 10mm head then yes it would be a M6 thread fitting. I keep a set like this, they are okay.

https://www.amazon.com/NEIKO-50467A...c+grease+fittings&qid=1757453022&sr=8-11&th=1

 

[Snagglefoot]

If it is 10mm head then yes it would be a M6 thread fitting. I keep a set like this, they are okay.

https://www.amazon.com/NEIKO-50467A-Assortment-Mechanical-Lubrication/dp/B0DYTMNZ8W/ref=sr_1_11?dib=eyJ2IjoiMSJ9._PRMfy2xdwb27hr_65T5kQCQHPreX57qXM12ASXMcSx16ASyrBlK4ClLc3p2XpLiAYWB7NzCZsVpRsxDZK8Q8a_CemCY-B_s086emyIhk0BpfIwLh7iaQIDLlWXbVLqZ37Hm8n1c8R7v8L0o6ZqOEk1cNoSLcfJ4XLImhjOGYrnUCuN9y_yulWGfttYhwgekT0tkZPERsBiU6M3jDmTv0iIHsHxRDR-aisJSyiGD3b4.xzK0zttwHCot10uU-P35pfChTZf8E-XI1NtZvriwYDY&dib_tag=se&keywords=metric+grease+fittings&qid=1757453022&sr=8-11&th=1

Thanks very much. My local hardware store had a pack of assorted 6mm fittings and I was good to go. There was not much room to get it started but it went in. The funny thing was the wrench to turn it in was 3/8", probably because it was just a cheap pack labeled Lubri Matic. I'll pick up a kit. I can always give it to my son.

 

[Snagglefoot]

One other thing I found is that the 1/4” 28 taper and the 6 mm fittings are almost the same size. There are also self tapping fittings that probably negate this issue. Using a calliper tool and measuring across the bottom of the threads of a 6M fitting yields 6.0 mm. Measuring across a 1/4 inch 28 taper yields some closer to a quarter inch which works out to 6.3 mm, very close to the metric one. Here are some shots of the digital calliper tool. Enjoy.