The difference between Mobil DTE named and numbered lubricants is the amount of anti-wear additives. Some older equipment might not be compatible with the higher levels of AW additives that newer machines require, so that is why both are offered. Both are used for machinery lubrication.
From my “The Practical Handbook of Machinery Lubrication” published by Noria (experts in machinery lubrication):
The functions of a hydraulic oil can be summarized:
1. Transmit power from one point to another.
2. Lubricate and protect the system components from friction, wear and contamination.
3. Transfer and disperse heat generated in the system.
4. Provide a seal and maintain pressure.
Hydraulic oil’s main focus is transmitting power, a lubricating oil’s main focus is reducing friction, so depending on the application, one might be better than the other. But, hydraulic oil is excellent at reducing friction provided it is offered in the required viscosity range and is used in many types of machinery for lubrication of bearings and gearing. Just because it has characteristics that make it better at transmitting power than industrial lubricating oils does not mean it is not suitable at lubricating bearings and gears. The most important characteristic of an oil selected for anti friction applications is it’s viscosity, the other features are a distant second. In the calculations for selecting an oil for bearing lubrication, viscosity is the only characteristic used.
The industrial centrifuge manufacturer I used to work for specified Mobil DTE 26 for lubricating bearings for machines running at 3,500 rpm as well as the cycloidal gearboxes used to drive the scroll drive. It functioned very well at lubricating the components, as well as removing heat from the bearings. We switched that to SHC 626 (a circulating oil) since in the larger machines in hot environments the bearings were running around 90c and dino oil was oxidizing quickly requiring more frequent oil changes. I don’t think anyone here is running their headstocks so hard that the bearings are reaching 90C and need a circulating oil.
All this talk about the differences between the different oil classifications is splitting hairs. Very few of us here use our machines in an industrial environment where the differences might make a difference. Select an oil with the right viscosity and anti wear additives and you will probably never notice a difference between Mobil, Shell, or even Tractor Supply oil in our lifetimes.