Base jacks and U-head jacks are both adjustable temporary-works components, but they serve different positions in an arrangement. A base jack is normally associated with the bottom support of a scaffold or shoring line. A U-head jack is normally used at the upper end to receive or locate the supported member.
They should not be treated as interchangeable simply because both use threaded adjustment. The end detail, bearing condition and connection to the surrounding system are different.
Vidaform lists these products within the Bases, jacks and wheels category. Final use must always match the approved system arrangement.
What does a base jack do?
An adjustable base jack provides a lower support and a controlled means of level adjustment. It sits between the scaffold or shoring member and the supporting surface or approved base arrangement.
The Vidaform catalogue identifies the principal adjustable base product as:
The catalogue also contains a non-adjustable Plain Base Plate — VID-BAS-PBP. A plain base plate and an adjustable base jack are therefore different products and should be scheduled by their exact codes.
Before selecting a base component, verify:
- The supporting surface and bearing arrangement
- Whether adjustment is required
- The system member that connects above it
- The permitted extension under the approved design
- Edge conditions, slopes and local obstructions
- The required inspection and restraint provisions
The jack should not be used to compensate for an unsuitable or unverified supporting surface.
What does a U-head jack do?
A U-head provides an adjustable upper interface shaped to receive a supported member. The Vidaform catalogue product is:
The U-shaped head helps locate the member at the top of the support line. The width, orientation, bearing and restraint of the received member still need to match the approved temporary-works detail.
Before selecting a U-head, verify:
- The type and dimensions of the member it will receive
- The direction of that member
- Required bearing and restraint
- The top-level adjustment required
- Compatibility with the vertical support below
- The extension and loading limits defined by the approved design
Base jack and U-head comparison
| Question | Adjustable base jack | U-head jack |
|---|---|---|
| Normal position | Bottom of a support line | Top of a support line |
| Principal function | Lower bearing and level adjustment | Upper adjustment and receiving a supported member |
| Vidaform example | VID-BAS-BJS | VID-BAS-UHJ |
| End shape | Base plate arrangement | U-shaped head |
| Can they be substituted automatically? | No | No |
This table explains functional position only. It is not a load-capacity comparison.
What about universal jacks and fork heads?
Vidaform also lists:
- Universal Jack 750 mm — VID-BAS-UNJ-0750
- Universal Jack 850 mm — VID-BAS-UNJ-0850
- Universal Jack 970 mm — VID-BAS-UNJ-0970
- Fork Head — VID-BAS-FKH
These are separate coded products. Their presence in the same category does not mean they have the same connection detail or application. Use the exact product code shown in the approved material schedule.
Information to include in an enquiry
For a useful quantity request, provide:
- The supporting system or vertical member
- Required lower and upper levels
- Supporting-surface information
- The member received at the top
- Required adjustment range from the approved layout
- Preliminary quantity by exact product code
The Vidaform formwork accessories page provides links to the relevant families. Quantities can then be selected in the catalogue and sent through WhatsApp without displaying prices.
Final selection reminder
Adjustment range alone is not enough to approve a jack. Final selection must account for extension, load, bearing, restraint, vertical alignment, compatibility and component condition. These checks belong to the project’s temporary-works design and site inspection process.
Browse the complete Bases, jacks and wheels catalogue before preparing the coded enquiry.