T-mount propellers are those that are based on a 1.5mm diameter centre shaft secured by a 2mm screw either side. They have been the only mounting option for 2-2.5 inch props but are now becoming more popular for 3" due to the weight they save over a 5mm single shaft prop mount. There are only 4 different types of t-mount 3" prop currently available so I've compared them all plus the new HQ 2 blade which is due for imminent release plus a darkhorse prop in a smaller size to make up the numbers. Please note this is a subjective comparison based on my opinion but my help as a startpoint for your decision. This is based on real world feel, light time and bitter experience with motors I've burnt out.

Emax Avan 3 inch tri-blade
This is the first modern design 3 inch prop designed for a t-mount which was released with the 3" Babyhawk R (reviewed here).

• Weight and Response: 1.27g This is very light for  tri-blade and mass is concentrated near the hub meaning response is very good for a triblade of this pitch.
• Pitch: Mid-range. This is well suited to 3s on an 1106 4500kV and will manage a 4s as well but is reasonably amp-hungry. Make sure your motors are not hot.
• Balance: Very good, typical of modern tri-blade
• Durability: Low-medium. Less material on the outer part of the blades means they bend/break easily, especially towards the edge of the blade
• Other notes: warning: given the unique design of the blade near the hub, this is unlikely to fit any motor with a stator size larger than 11mm. Update: confirmed these fit successfully without modification on the RCX 1304. New RCX 1306 unconfirmed.
• Recommendations: Excellent on 3s but be cautious on 4s considering this is limited to 13mm stator size
• Available from: Banggood, Hobbycool

Dark horse to consider...

Others:
Please note the King Kong 2840 propeller was not included here because I found the Gemfan 2540 superior in every way. Also I have not include the Rotor X 3044 because it is difficult to source where I am based. The feedback that I have had is that it is more aggressive in pitch than any of the above props and probably only suitable for for stator sizes 13xx and up.​

Gemfan have recently released the 2540 Flash propeller to add to their growing library of micro propellers. This time rather than sticking with their 'Hulkie' naming on the 1940 and 2040 propellers, they have gone with 'flash' from their popular 5" 5152 prop.

The design is stylistically similar to the 5152 in that it is a swooping 3 bladed propeller with a pronounced wingtip. Colours currently available as below. I like the yellow as they are easy to find!

The material feels very much the same as the gemfan 2040 Hulkies which I reviewed here but the design is much more refined and so will not make any further comparisons as design will impact performance and durability more than material.

For testing I used my Leader 120. This is a popular model and I have put 80 odd packs through this one making it a good test mule. Also, I have experimented with other props like the Gemfan 3025 alongside the stock King kong 2840 for more than one point of reference.

Since this frame will fit a 2.8 inch 2840 prop there is plenty of room on a 2.5 inch 2540 without losing too much blade area. No issue installing so will move on to flight performance.

Performance on 2s
The first thing I noticed about these props is that they were very quiet. I flew in a reserve where there were several people enjoying the sun and very few people even noticed the quad flying about. The noise made was even less than the 2840s which are already very quiet. On 2s the performance was almost on par with the 2840s. I was able to hover at around 25% throttle with a 47g 950mah 2s battery and had flat out speed close to the 2840s. Cornering (grip) felt about 90% as good as the 2840s which is the grippiest quad/prop I have - even more than my 5" racing floss 2. Balance was excellent with no increase in jello at high throttle over the 2840s which have always been well balanced for me.

Battery life was definitely superior to the 2840 props. As you'll see from my pics below I got around 6 minutes from the 950mah battery with fairly heavy throttle flights as I was in a large reserve. This is about a minute more the the king kong 2840s with similar flying and comparable times to the Gemfan 3025 (although the 3025s were slower on 2s). It was an enjoyable 6 minutes too - the quad felt tight with these on.

 Performance on 3s
For 3s testing I used my Turnigy Nantoech 3s 450mah 65C batteries that weigh approximately 45g.

The performance gap between the stock 2840 and new 2540 propellers were even less pronounced than on 2s. If there was a difference in performance compared to the 2840s in top speed or cornering grip I could not tell. The advantages did remain though - 2540 propellers were again more quiet and I had a similar increase in battery life: from roughly 3 minutes of hard flying to roughly 3.5 minutes+ hard flying (see below). Lastly at higher RPM I actually had less jello than any prop I have used on this quad before. This suggests they have excellent balance.

In short I got all of the benefits I enjoyed on 2s with none of the downsides.

Durability
Oddly enough I haven't had a crash worth speaking of yet. I'll update here once I've had a view and can give more of an opnion on this.

Conclusion
Simply put these are now my favourite prop on both 2s and 3s for the Leader 120. I can only guess that the more modern design helps get the efficiency up over the 2840 on 2s with very nearly the same top speed and grip through corners. On 3s the gap was even less and I'd struggle to tell the difference between these and the 2840s. The only real change was that there was less noise and more flight time.

In conclusion these will be my go-to prop from now on my leader 120 on 2s or 3s. The slight downside of marginally less top speed and cornering grip is easily outweighed by the reduced noise and improved battery life. Give them a try for yourself, they are inexpensive.