In Pairs Harness, breeching straps form a link between the breeching ring and breastplate. 

These 25m (1") breeching straps are suited for use with Classic and Elite Pairs Harness. The slot end is fitted to the breastplate buckle, underneath the trace. 

The other end of the strap is attached to the breeching ring via the use of a loose bukle piece https://www.chandellessaddlery.co.uk/ourshop/prod_3061030-Loose-Buckle-Piece.html

 which is purchased separately. 

Length: 89cm (35") 445071
Pony Size 

Length: 104cm (41") 445074
Cob Size 

Length: 119cm (47") 445075
Full Size 

these are a special order and it is 14 days for delivery