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To calculate the button diameter of a bolt, you do not multiply the thread size by a ratio. On a button head bolt, "button diameter" means the maximum outside diameter of the rounded head, shown as dk on drawings. You read dk from the governing standard, such as ISO 7380-1, for your thread size. Then you check that value against your clearance, tool access, and bearing area. This guide walks through each step, from size charts to M6, M8, and M10 examples, and shows where Grade 5 titanium fits.
What Does "Button Diameter" Mean on a Bolt?
Head Diameter Versus Thread Diameter
This is the button diameter, which is the largest point across the head's dome. On technical models, it is shown as dk (sometimes Dk). The nominal thread diameter is the number in a name, like M6 or M8. This is not the same thing. It is also different in terms of overall length, thread length, head height, and socket width across flats. In a normal table, each measurement has its own column. A lot of the time, buyers get the head size wrong when they try to guess it from the shank. This is because the head size comes from the standard, not a set multiple. Every time I write a document, I treat dk as a separate entry. I think you should do the same.
Button Head Bolt and Button Head Socket Screw Terminology
Suppliers give parts that are very similar more than one name. What do "button head bolt" and "button head socket screw" mean? They usually mean a head with a dome shape and an internal hex drive. A "low-profile socket screw" can also mean a flat cap screw, and some buyers look for a "button head cap screw." It is more important that the picture than the name. Parts that are sold in the US under the same name might not be made the same way as parts that are sold in Europe under the same name. I suggest that you match the product name to a standard number, a drive type, and a thread system before you list or order it. This way, everyone will read the same part.
Standards That Define Button Head Bolt Dimensions
Most button head bolt sizes are set by three sources. You can find hexagon socket button head screws in ISO 7380-1, and the version with a cap is in ISO 7380-2. ASME B18.3 covers socket items in the inch line, such as button head cap screws. Both can be pushed aside by your own drawing. It is possible for these papers to show different standard sizes for heads, sockets, and tolerances, so I never mix the tables. The head type on our titanium button head bolts is ISO 7380, and our material standards are ASTM B348 and ASTM F136. If you include the standard in your listing or purchase order, you can track every dimension that comes after.
How to Measure, Read, and Calculate Button Head Diameter?
Step 1: Identify the Required Bolt and Head Dimensions
Start with a full list of dimensions, not just the thread name. Use a calibrated caliper to measure the largest diameter of the head. Take two or three readings at different angles and then average them because coatings and curved heads can change a single reading. Then write down the total length, the thread length, the socket depth, the socket width across the flats, and the head height. I look at the supplier's drawing line by line and compare these numbers to them. Thread size and pitch, dk, head height, drive size, length, material, and finish are all good things to write down on a short list. This check makes sure you don't pick a fastener based on the thread number alone, which is a common mistake that leads to samples that don't fit when they come.
Step 2: Use the Correct Button Head Bolt Size Chart
In order for a button head bolt size chart to work, it must first be named. For hexagon socket parts in metric units, use the ISO 7380-1 table. For inch units, use the ASME B18.3 table. A useful metric chart shows the sizes M4 through M12, which includes the common M6, M8, and M10 ones. For inch parts, write down the size, like #10, 1/4 inch, 5/16 inch, 3/8 inch, or 1/2 inch, and the thread type, like UNC or UNF. We have threads from M3 to M24 in metric, UNC, UNF, and custom sizes. It is not safe for me to copy numbers from web charts that aren't labeled because they might mix up standards. Get the numbers from the official table and send one copy with your order.
Step 3: Calculate the Required Button Head Diameter
The math is a check for fit. First, get a DK from the rule. Then, make sure that the largest head diameter that your design allows is at least as big as the head you choose: dk, required ≤ dk, available. Check D clearance ≥ dk + 2c to see if the head fits into a groove or goes through a hole. Here, c is the radial gap you leave to account for error, coating thickness, and movement of the unit. If the parts swell and shrink a lot, add thermal expansion. Watch out for edge distance, nearby parts, tool access, and bearing area as well. Some other types of screws might work better in this joint if the dome is too small to spread the load. These are the washer, collar, and socket head cap screws.
Worked Examples and Strength Checks for M6, M8, and M10
Work Through an M6 Button Head Bolt Example
Let's say you need an M6 button head bolt for a frame that isn't very tall. You need an internal hex drive, something that won't rust, and a thread length that stays the same. Take the M6 row from the official table and read dk, head height, and socket size. Then choose ISO 7380-1. Make sure that dk fits the recess and that you have enough space c. Make sure the hex key fits into the socket at the right angle for the assembly. After that, look over the torque and strength. Ask for an inspection report and a sample to be approved before starting to make a lot of them. I always do things in the same order, no matter what size.
M8 and M10: Why a Larger Size Does Not Settle Everything
Moving from an M6 button head bolt to an M8 or M10 button head bolt makes the head bigger and the thread stress area bigger. Even if the number is bigger, that doesn't mean there is enough preload. Socket head cap screws have a deeper hex socket than button head cap screws, so the drive can stop the force before the thread does. The material being clamped can also change the bearing area under the head. For example, an M10 head may need a washer on a soft aluminum plate. For every size, I check the dk fit, socket access, material strength, and bearing area the same four times. Put the results next to each other and pick the smallest size that works for all four.
Check Strength and Torque for Grade 5 Titanium
The diameter of the head does not determine its strength. So do the loading, the thread stress area, the material, and the heat treatment. ASTM B348 says that Titanium Grade 5 (Ti-6Al-4V) must have a tensile strength of at least 895 MPa. Its density is about 4.43 g/cm³, which is about 44% less than steel's density of 7.85 g/cm³. T = K × F × d is what engineers use to find torque. K is the nut factor, F is the preload, and d is the nominal diameter. It is important to try your own system because K changes with friction, coating, and lubrication. Titanium threads can get stuck, so use an anti-seize solution or ask for a covering. A socket head cap screw might be needed for joints with a lot of preload.
Compare Options, Choose Materials, and Avoid Errors
Compare Button Head Bolts with Other Fasteners
Different types of heads are good for different things. A button head bolt works well for small, visible, moderate-load parts. Because its socket is deeper and its head is taller, a socket head cap screw can usually hold more preload. This type of bolt fits perfectly because it has a countersunk hole and is thick enough. A hex head bolt fits into gaps and has a bigger area for bearing. There is less height with a low-profile socket screw, but the socket may not go as deep or hold as much force. Place the joint on top of the head. If you care about looks, snag resistance, and low height, choose the button head. If the joint needs the most clamp load, choose a different style.
Select Material, Finish, and Thread Type
Pick a material based on cost, space, and load. Stainless steel A2 and A4 can be used outside and in wet places, but they are heavier and can rust. Strength is the most important thing in machinery, so alloy steel with black rust works well. Titanium Grade 5 is good for parts that need to be light and resistant to corrosion, like bike parts, motorbike parts, and naval gear. This is because titanium makes a stable oxide layer that doesn't react with seawater chloride. You can polish the finish or make it look like the drawing. Mesh and imperial threads should not be mixed. In every purchase specification, make sure you check the diameter, pitch (threads per inch), tolerance, length, drive size, material grade, and finish.
Avoid Common Selection Errors
There is a short list of habits that cause most of the problems. If you guess the head diameter from the thread size, you'll get the wrong spacing. You can't tighten a bolt after checking the clearance but not getting to the tools. If you use a button head on a joint that needs a lot of preload, the head could deform, the socket could become stripped, and the bearing could fail. When you copy an online torque table, you don't take into account things like friction, grease, coating, or material grade. If you don't include standards, tolerances, certificates, and labels, there could be problems after delivery. Before every order, you should quickly go over these five points. In just a few minutes, it stops returns, extra work, and bad reviews from customers.
Specify and Source Titanium Button Head Bolts
How to Specify Button Head Bolts in an RFQ
An exact RFQ line takes the guesswork out of it. Type of fastener, standard, thread size, length, material, finish, thread coverage, quantity, and documents needed should all be included. Here is a sample line: "Button head socket screw, ISO 7380-1, M6 × 20 mm, Titanium Grade 5, full thread, polished." Place of delivery, expected number, wait time, minimum order, packing, and labeling needs should all be listed. When you test a new listing, ask for the drawing, the inspection report, the material certificate, and a sample. They can quickly quote and ship the right part the first time if you give them clear information.
Wisdom Titanium Grade 5 Button Head Bolt Specifications
Here are the details of the product I give to buyers who want to try a new ad with few sales. With a minimum order of 100 pieces, we offer titanium button head bolts that are ready to ship. We also keep raw materials and standard parts in stock at stable prices. The item is made of Titanium Grade 5, and the standard is ASTM B348, ASTM F136. The size range is M3–M24, and the thread type can be UNC, UNF, Metric, or custom. The head type is a button head ISO 7380, and the surface finish can be polished or as specified by the customer. Because it has metric, UNC, and UNF threads, you can use the same source to make different types of button head bolt M6, M8, M10, and different lengths. Tell us about the different sizes, the packaging, and the labels, and we'll let you know what we can do.
How a Button Head Bolt Manufacturer Supports Custom Requirements
A lot of designs don't work with standard parts. Custom needs can include a head diameter that isn't standard, a lower head, special sockets like security Torx, a thread length that isn't standard, or a PVD coating. Head diameter is limited by the size of the bar stock and the depth of the drive. A very wide, short head can leave a shallow hole that cams out, so heads that are more than 1.5 times the normal ISO diameter need to be looked at by engineers. Send a sketch or the full specs. Baoji Wisdom Titanium Industry and Trading Co., Ltd is a manufacturer in Baoji Titanium Valley, Shaanxi Province, that has been in business since 2016 and is ISO 9001 certified. This is the biggest titanium industry cluster in China, and our own R&D team makes parts from samples or ideas you give them.
Conclusion
The button diameter of a button head bolt is its largest head diameter. This value comes from the standard and not from a ratio to the thread size. The math is a check for fit. We will measure the sample, look at the ISO 7380-1 or ASME B18.3 table, and then compare dk with the bearing area, edge distance, clearance, and speed of access. The M6, M8, and M10 examples showed that a bigger size doesn't always mean more preload because torque is limited by socket depth, material, and friction. Titanium Grade 5 has a minimum tensile strength of 895 MPa and weighs about 44% less than steel. However, it needs to be treated to keep it from seizing up. When you compare head types, pick out the material and finish, and write a full specification, you cut down on mistakes and returns.
FAQ
Is the diameter of the button head the same as the diameter of the thread?
Not at all. The shank size is given by the thread diameter, like M6. You can get the head width, dk, from ISO 7380-1, ASME B18.3, or the supplier's drawing.
Are a button head socket screw and a button head bolt the same thing?
In business, the terms are often used interchangeably, but the names change from place to place. Before you buy, make sure you know the standard, thread system, and drive type.
Do titanium button head bolts work with parts that are under a lot of stress?
Grade 5 must have a tensile strength of at least 895 MPa, but the short hex socket often stops the force before the thread does. It is best to use a socket head cap screw or test your own assembly for high-preload joints.
Can I order button heads in any size I want?
Yes. Send a drawing with the size of the head, its height, its socket, its thread, and its finish. Before giving the go-ahead, we look over the feasibility, tooling, and minimum order.
Request Button Head Bolt Quotes from Wisdom Titanium
Wisdom Titanium is a company that makes bolts. They ship Grade 5 titanium button head bolts in sizes from M3 to M24, and they always have 100 in stock. Send your drawing, size, quantity, and delivery address to sales@wisdomtitanium.com. We'll let you know if the product is available, what the dimensions are, and how long the lead time is. Ask for samples and paperwork for inspections. For more information on this product, go to wisdomtitanium.com.
References
- ISO 7380-1: Fasteners — ISO Button Head Screws — Part 1: Hexagon Socket Button Head Screws, 2011
- ASME B18.3: Socket Cap, Shoulder, and Set Screws, Hex and Spline Keys (Inch Series), 2012
- ASTM B348/B348M: Standard Specification for Titanium and Titanium Alloy Bars and Billets, 2019
- ASTM F136: Standard Specification for Wrought Titanium-6Aluminum-4Vanadium ELI Alloy for Surgical Implant Applications, 2013
- Machinery's Handbook, 31st Edition, 2020
- Introduction to the Design and Behavior of Bolted Joints, 4th Edition, 2007
