Refer to the Shimano website for diagrams and specs
exploded diagram via
Steel Ball (1/4") 18 pcs
Left Hand Seal Ring
Right Hand Seal Ring
As you can see there and here
compared with the cheaper FH-T3000
If you refer to the full parts list & spec you can see that the axle is the same, but other parts are different, including more/better seals on the T610
Some other bits from the spec:
- CBN - cubic boron nitride - refers to the finish on the bearing race (Shimano only)
- Free hub body - steel this makes it heavier, but the design of HG freehub bodies means steel is usually better because the splines are vulnerable when using (more expensive! aluminium)
Shimano have discontinued the higher spec T780, which uses smaller ball bearings.
This is generally reckoned to be Shimano's most durable design:
the FH-M756; note that there is a new, downgraded version, FH-M756A.
M756(A) uses a large flange diameter, which makes the wheel stronger (with reference to things like spokes breaking). It's quite heavy, compared to newer designs.
- M756 is a six-bolt disc hub, the others listed are centerlock, so that's an issue for those with centerlock discs as you'd need an adapter
- Your T610 is way above the quality of standard $800 bike freehubs, which will tend to be more like the T3000 I linked above, or even cheaper versions with worse sealing https://si.shimano.com/api/publish/storage/pdf/en/ev/FH-RM35/EV-FH-RM35-3250A.pdf
- People telling you to get sealed bearings (presumably cartridge bearings) are simply wrong - cartridge bearings are a valid choice, and they are easy to replace as they are a cartridge rather than loose balls, but they are not better per se. Rather, 'boutique' hub makers will have lower manufacturing costs with cartridge bearings, compared to Shimano producing loose bearing freehubs. So there are lots of people with a vested interest in promoting cartridge bearings.
- Lots of expensive freehubs are prone to failure as they are sold on lightness, not strength, and the use of aluminium on freehub bodies and axles makes them much less durable than a quality Shimano loose bearing unit made from steel.
- Very expensive Shimano freehubs have more and smaller balls, which won't help durability but perhaps shaves off weight.
- A Shimano freehub is designed to be packed with lots of marine grease, so that it rejects water.
- Modern Shimano freehubs of 'M' type are sold on weight and 'degrees of engagement', a marketing feature referring to how quickly the freehub mechanism engages when you start pedalling on the edge of the precipice of doom. They are often less durable than older mechanisms; it's not sufficient to merely look at the 'groupset'.
- Your T610 looks fine, but you will need to rebuild the wheel. It could be better just to buy a pre-built wheel with a better freehub built in to it.