Looks like a slidelock fuse, used to use them on the meter dept of the DNO I used to work for to protect contactors, also used in street lights, Bussmann make a similar one.

Looks like a slidelock fuse, used to use them on the meter dept of the DNO I used to work for to protect contactors, also used in street lights, Bussmann make a similar one.

I live and learn, Google actually suggests a different spelling 

www.thefusecompany.com/.../k511fw-5amp-415volt-slydlok-fuseholder-black-k-range.php

To be honest Sparkingchip I never looked at them in detail just grabed a handfull when I was geting low in the van so never knew the correct spelling;