These demolition charges exist in a serie of 4 types.

SZ-1 : 65x116x126mm , 1kilo TNT, 1.4kilo total weight.
SZ-3 : 65x171x337mm , 3kilo TNT, 3.7kilo total weight.
SZ-3a: 98x142x200mm , 2.8kilo TNT, 3.7kilo total weight.
SZ-6 : 98x142x395mm , 5.9kilo TNT, 7.3kilo total weight.
SZ-6m: looking for information

Information thanks to Jarda Mattás.
All scans thanks to Preben.

SZ-1 & SZ-3 :

SZ-3a :

The SZ-3a charge was also to be used for underwater demolition op to 10meter deep.
The charge holds 2.8kilo cast TNT or TNT/RDX and the booster is compressed TNT.
When it was used underwater, it was fitted with the VPZ-1 fuze and detonator No.8
For land-use it was fitted with the electric EDP-r detonator.
Rubber straps with hooks were used to fix the charge to the object.

The charge in the photo bears the text "
INERTN" , which means that this was an empty trainer.

Information thanks W. Jordan.
Photos below © Marcin.

SZ-6 :

SZ-6m :