If you are buying scaffolding accessories for the first time, the “size” of a U-head jack can be confusing. Unlike a standard pipe, a U-head jack is described by three measurements at once: the diameter of the threaded stem, the length of that stem, and the size of the U-shaped plate on top. Get any one of them wrong and the jack simply will not fit your system. In this guide, we break down the u head jack scaffolding sizes that are actually available, what each number means, and how to pick the right u head jack size for your project.
How U-head jack sizes are described
A typical u head jack specification looks like this: 38 x 600mm with a 150 x 120 x 50 x 5mm plate. The first figure (38mm) is the outer diameter of the threaded screw rod. The second figure (600mm) is the overall length of the rod. The final figures describe the U-head plate itself: 150mm long, 120mm wide, 50mm deep, and 5mm thick. Some suppliers list the plate size first and the rod second, so always confirm which measurement is which before you order.
Threaded stem diameters
The threaded stem diameter is the most important dimension, because it must match the inner diameter of the vertical tube it sits inside. In practice, most u head jack scaffolding uses stems between 26mm and 48mm in diameter. The most common sizes are 30mm, 32mm, 34mm, 35mm, 38mm and 48mm. For example, Bythai’s adjustable u head jack for the tube and clamps system uses a 38mm hollow rod, while their solid base jacks come in 30mm, 32mm and 34mm versions.
Stem lengths
The stem length controls how much height adjustment you get. Standard lengths range from 400mm to 1000mm, with 400mm, 500mm, 600mm, 750mm, 800mm, 900mm and 1000mm being the most frequently requested. A 600mm jack is the most popular choice for general construction because it offers a good balance between adjustment range and stability. Longer stems give more fine-tuning but reduce the overlap inside the tube, so they are usually reserved for shoring and formwork work.
Solid vs hollow U-head jacks
U-head jacks come in two basic types: solid and hollow. A solid jack uses a full steel rod, which makes it stronger and better suited to heavy loads, but heavier to handle. A hollow jack uses a tube, so it is lighter and easier to transport, and it is the standard choice for tube and clamp systems where the jack sits inside a 48.3mm tube. The hollow type is also common in ringlock and cuplock shoring towers. As a rule, choose solid for high-load applications and hollow when weight and handling matter more.
U-head plate sizes
The U-shaped plate on top carries the timber or steel beam, so its width should match your beam width. Common plate sizes include 150 x 120 x 50 x 5mm and 150 x 185 x 50 x 5mm. Bythai’s u head jack for tube and clamps uses a 150 x 120 x 50 x 5mm plate, which suits standard timber and H20 beams. If you are supporting wider beams, a wider plate is available on request.
Thread pitch and finishing
The thread pitch also matters. Most standard jacks use a 6.35mm pitch, while coarse-threaded (fast-thread) jacks use an 8mm pitch. Fast threads adjust more quickly, which saves time on large sites, and they also take a thicker galvanized coating. If you are ordering hot-dip galvanized jacks, ask your supplier whether the thread is cut before or after galvanizing, because this affects how smoothly the nut turns.
Matching the size to your scaffold system
Before you choose a size, check which scaffold system you are using. A u head jack for a tube and clamps system normally has a 38mm or 48mm hollow stem that fits inside the 48.3mm tube. Ringlock and cuplock systems use jacks with a stem that matches their rosette and cup dimensions, usually 38mm for ringlock and 38mm for cuplock. Frame systems commonly use solid jacks from 30mm to 35mm. If you are unsure, send your vertical tube’s inner diameter to the supplier and they will confirm the correct stem size.
Quality and coating
Size is only half the story. A u head jack is only as good as the steel it is made from and the coating that protects it. Look for Q235 or Q355 steel, and choose hot-dip galvanized, electro-galvanized or powder-coated finishes depending on your environment. Hot-dip galvanized is the best choice for outdoor and coastal sites because it offers the strongest corrosion protection. Bythai manufactures its jacks in accordance with EN and BS standards and can provide ISO9001-certified quality documentation with every order.
How to order the right size
When you are ready to order, give your supplier four things: the scaffold system you use, the stem diameter and length, the plate size, and the surface finish. Most Chinese manufacturers, including Bythai, offer flexible MOQs and OEM customization, so you can have jacks made to your exact specification rather than settling for a standard size. This is especially useful for distributors who need consistent sizes across multiple projects.
To sum up, u head jack scaffolding is available in a wide range of sizes, but the three numbers that matter are stem diameter, stem length and plate size. Match them to your system and your beam width, choose solid or hollow based on your load and handling needs, and pick a finish that suits your site. If you are not sure which size you need, contact Bythai with your system details and they will recommend the right adjustable u head jack for your project.