These are the split brass washers that are soldered to the end of the HT lead that is screwed into Lucas and other similar magnetos that use screw in HT connections. These are genuine Lucas items. Price is for pack of 4.
Using these washers give a good connection and retains the HT lead behind the bakelite/plastic screw in Lucas 'acorn' connector. I always solder the copper HT lead to the washer, then grind away excess solder, to ensure best connection (I have found over the years that oil and grime can leak into Lucas screw in HT connectors - if the HT lead is left unsoldered to the washer this gets clogged in oil and reduces connection). I show the acorn in the second photo - but please note this listing is for the brass washers only