Our resident expert, Cliff Billington is here to answer your burning questions about techniques and correct practices within the concrete industry.
If you have a question for him, get in touch...
 

Cliff is here to help you with your construction conundrums, your precast problems and your building brain-teasers. 
Submit any questions you have, and we’ll do our utmost to get them answered as soon as possible!

First up, Pete asks:
What is the difference between Rd and Metric thread?

 

Pete:

The common, everyday, type of thread is metric, and this has many uses, including fixings to attach precast concrete on to a structure. If a lifting system has the same thread configuration then it is possible to screw a lifting head into the socket intended for fixing. This can have serious consequences on safety, and in the 1970s a new type of thread was devised for lifting systems. This is known as a round thread, Rd for short, and as the name implies, the thread is rounded rather than the sharp profile in a metric thread. The pitch of the thread is the same, but the slope of the thread is steeper than metric.

As a result, although it is possible to screw a metric insert into an Rd socket, it is not possible to screw an Rd insert into a metric socket. This prevents accidental errors during lifting. Some suppliers still provide metric lifting systems, but generally Rd is the norm.

The difference is illustrated in the data sheets on ‘Lifting inserts’ in Key2concrete, which can be found by clicking here.

  
 

 

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