Peters Spares PS51 Replacement Mainline Large Round Buffers (Pk4) Blackened Metal, These Measure 5.8mm in Diameter
OO Gauge
These are replacements made by Peter Spares in the UK.
(Items will need to be removed from the metal mould sprue, this can be done with a good pair of snips or fine modelling saw or even a electric mini drill with slitting / cutting disc. The items can then be glued into place using superglue. You may see a small mout of green on the item, this is oxidisation of the bronze and will wipe off. This can be stopped by spraying or painting with a varnish.)