What is inside Thorens MM008 adapting jacks for MC input

I bought a used phono preamp Thorens MM008 like this
Thorens MM008 phono preamplifier - maPlatine.com


Unfortunately the jacks with the appropriate resistive loads (10, 100 and 1 Kohms) for adjusting the MC input are missing.
https://www.maplatine.com/en/4687-thickbox_default/thorens-mm008-phono-preamplifier.jpg


Does someone know what is exactly inside these jacks? Only resistors 10, 100 and 1 Kohms? Or is there more or anything else inside?


I want to make these by myself.


Please let me know. Thanks.