Not very elegant but Decathlon do one you could shim
http://www.decathlon.co.uk/EN/l330-basic-diam-23-4-25-27-2-35412401/
@andydale started
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Not very elegant but Decathlon do one you could shim
http://www.decathlon.co.uk/EN/l330-basic-diam-23-4-25-27-2-35412401/