Ericsson headphones. Aluminium earpiece casings and headbands black earpieces, original flexible leads 4000 ohms, made in Beeston Notts, UK. Apart from being a higher impedance than the SG Brown headphones also on this site these are of a more robust design and more comfortable to wear. The other advantage as indicated below is that there are no exposed terminals. Of course with a crystal set this is of no consequence but the situation could be rather different when the phones are connected in the anode circuit of a valve radio where these terminal may be 150 volts above earth potential! I understand that this type was used by the BBC.
close up view of one earpiece.
Here is a picture and description from a 1934 trade catalogue. Mine belonged to my father so the would have been purchased back in the late 1930's.