NCV2.1 clock kits are provided with 20mm spacers and connector which does not require any custom work.
This item is for those who want to stack both PCBs using 15mm spacers.
The price is for four 15mm spacers and connector rail. These spacers ensures thin design of NCV2.1 nixie clock but requires custom made connector (look at document below). Fit for both IN-14 and IN-18 versions.