Steel, aluminium and titanium are the popular materials used in FPV drone fasteners. The weight differences are fairly significant which might have a noticeably impact on flight performance. Steel is the heaviest for a reason, it’s tough and durable, but there are also different grades to choose from.
Table of Contents
TL;DR
Here’s a summary of the post:
- Hex screws are the most popular type of fasteners for FPV drones (looking for hex screw drivers? check out this post)
- Use socket head screws for mounting the motors; Use button head on the rest of the drone e.g. frame, stack etc
- For durability and low cost, use steel; For light-weight, consider titanium or even aluminium
- Alloy grade matters when it comes to durability
Button Head vs Socket Head
Socket head cap screws typically offers higher tensile strength, better yield strength, and more shear strength than equivalent sizes of button head cap screws. But button head screws are slightly lighter and have a lower profile than socket head.
Socket head screws are used where maximum tensile strength is essential, for example on the motors where threadlocker is often applied.
Button head screws are ideal for lighter applications where loading capacity is not critical, and are great for saving weight. For example on the frame and FC/ESC stack. Because they have a lower profile, it has less chance of digging into your LiPo battery in a crash than socket head screws when used on the LiPo mounting side of the frame.
Weight Differences
Here’s a weight comparison between aluminium, titanium, steel and stainless steel screws. Measurements are taken from a kitchen scale, so use them as reference only.
M3 6mm:
- Nylon (cross) 0.07g
- 7075 aluminium (button) 0.17g
- 7075 aluminium (socket) 0.24g
- Titanium GR2 (button) 0.26g
- Stainless Steel (button) 0.45g
- Steel 10.9 (button) 0.49g
- Steel 12.9 (button) 0.52g
- Steel 12.9 (socket) 0.66g
M3 8mm:
- Nylon (cross) 0.09g
- 7075 aluminium (button) 0.20g
- Titanium GR2 (button) 0.33g
- Stainless Steel (button) 0.50g
- Steel 12.9 (socket) 0.74g
Strength Differences
I googled these numbers, can’t verify how true these are since there are many variables. Take it as a grain of salt.
- Tensile Strength: The maximum load in tension (pulling part) which a material can withstand before breaking or fracturing.
- Yield Strength: A measure of how much the fastener will take for it to deform by around 0.2%.
| Ultimate Tensile Strength | Yield Strength | |
| Steel 12.9 | 1200 MPa | 1080 MPa |
| Steel 10.9 | 1000 MPa | 900 MPa |
| Stainless Steel A2/A4, 80 | 800 MPa | 600 MPa |
| Stainless Steel A2/A4, 70 | 700 MPa | 450 MPa |
| Titanium Grade 5 | 950 MPa | 880 MPa |
| Titanium Grade 2 | 344 MPa | 410 MPa |
| Titanium Grade 1 | 345 MPa | 220 MPa |
| Aluminium 7075 | 228 MPa | 103 MPa |
| Aluminium 6082 | 130 MPa | 85 MPa |
| Aluminium 6063 | 100 MPa | 50 MPa |
Steel Grades
Common grades for steel bolts are 10.9 and 12.9. Those numbers are the “property class” of the bolt, and they are usually only applied to regular carbon steel hex head cap screws.
The first number represents the tensile strength of the screw in megapascals. The second number represents “Yield strength” which means the tensile force that will cause a permanent change to the shape (and microscopic structure) of the screw.
In a nutshell, Bigger Number = Stronger Fastener.
12.9 grade steel has 120% of the tensile strength of 10.9 grade steel. 10.9 screws appear to be a tiny bit lighter in my weighing.
Stainless Steel Grades
Common grades are A2 and A4, both are usually non-magnetic.
A quick google reveals that A4 has the added bonus of being suitable for marine solutions, with better corrosion resistance to withstand attack from many industrial chemicals and solvents and chlorides. But both have similar strength and durability, and are equally good for FPV purposes, so get whatever is cheaper for you.
Sometimes there’s a number after A2/A4, e.g. 70 or 80, which denotes the minimum tensile strength to be met by the material.
Pro Tip: Some stainless steel fasteners are not magnetic, make sure you check before buying if this is important to you. Or just use steel.
Aluminium Alloy Grades
There are two common types of aluminium alloy used in FPV: 7075 and 6082. The number designates the different series of aluminium alloy grades and chemical composition.
In a nutshell, 6082 has more ductility and is more formable while 7075 is more rigid and hold up better against crashes. 7075 is more suited for our application.
Titanium Grades
Between Grade 2 and Grade 5 primary difference is strength.
A titanium grade 5 fastener is approximately 2x stronger than grade 2, and the Grade 5 offers a yield strength of 138ksi versus 50 ksi of grade 2. Due to the alloy content, grade 5 is more expensive than grade 2.
In general, grade 2 is the utilized for corrosion related applications, whereas for application requiring high strength, we would recommend grade 5.
Between Grade 1 and 2, Grade 1 is slightly weaker, lower tensile strength, but it’s one of the softest titanium grades that make it highly formable. The grade 1 is widely used where a high level of formability and weldability is necessary.
Drone Fastener Recommendation
Although nylon screws are the lightest, I’d avoid using them as they break easily in crashes.
For maximum strength and durability, use either steel or titanium. However, titanium screws are usually 5 to 10 times more expensive than steel, despite the estimated 50% weight saving.
On a 5″ FPV drone, all the steel screws would weigh around 21.5g (only an estimation: stack 6g, motors 6.5g, frame 9g). If we were to replace them with all titanium screws, we could save about 10-11g. It might sound a lot, but that’s only 1.8% of the total weight of a 5-inch FPV drone which typically has an all up weight of over 600g.
To pay $20-$30 extra on titanium screws for the less than 2% weight saving might be excessive for most people, personally I don’t think it’s worth it for a typical drone build. But for hardcore pilots like racers and premium freestyle builds where you try to squeeze as much performance as possible, titanium screws are great options.
I generally would avoid aluminium fasteners, they are just way too easy to strip, and when that happens they are a pain to remove. However, for extreme weight saving (e.g. racing drones), I’d put aluminium screws all over the quad where strength doesn’t matter, you could potentially save 67% weight compared to steel. However I’d never use aluminium bolts for mounting motors, after you apply threadlocker they are very easy to strip when you try to unscrew them. But by using aluminium screws for the frame and stack and titanium screws for the motors, you could possibly save 13.3g on a 5″ quad! (only an estimation)
Socket head bolts are slightly heavier, but in my experience less likely to strip. I tend to use socket heads on motors (because I normally apply threadlocker on those screws and they require more force to remove), the rest I normally use button head for the small but meaningful weight saving.
To avoid screws touching motor winding, choose the screw length based on the thickness of the arm and motor base. Screw length 2mm longer than the thickness of the arm usually work well. E.g. 8mm screws for 6mm arms.
Pro Tip: You don’t always have to use metal fasteners. In some cases you could just use zip ties, for example to hold down the VTX or Vista. It’s much lighter and secure enough, suitable for things that don’t care about vibration unlike the FC.
Where to Buy?
All these links are affiliate links, they don’t cost you any extra but when you make a purchase using these links I receive a small commission which will help to keep this blog going.
Titanium
- All selections (AliExpress): https://s.click.aliexpress.com/e/_DlnZ4aF
- All selections (Amazon): https://amzn.to/3rYFdjR
- M3 6mm (GetFPV): https://oscarliang.com/product-hvsb
- M3 8mm (RDQ): https://oscarliang.com/product-od6f
- M3 20mm (GetFPV): https://oscarliang.com/product-yfza
- M3 25mm (RDQ): https://oscarliang.com/product-doyz
Steel
- All selections (Amazon): https://amzn.to/3MOukLf
- M3 6mm/8mm/10mm/12mm (BG): https://oscarliang.com/product-y3yj
- M3 20mm (GetFPV): https://oscarliang.com/product-dv47
- M3 30mm (GetFPV): https://oscarliang.com/product-3a7x
Stainless Steel
- All selections (Amazon): https://amzn.to/3Cydn2R
- M3 6mm/8mm/10mm/12mm (BG): https://oscarliang.com/product-0d1x
- M3 5-20mm (RDQ): https://oscarliang.com/product-daof
1 comment
This is the best resource for FPV on the internet. So much detail and well explained to noobs like me. Thank you for all the work! Just subbed to your patreon.