You will never have to search for tools to make a shroud tension change again.
These shroud keys for your Etchells are a double ended Derlin key with 5/16 in. wide slots to hold the upper and lower shrouds at the swedge simultaneously. Slide onto flat spot on threaded shroud adjuster studs on the upper and lower shroud.
Using rigging tape keep them in place and there is no further need for a tool to hold the stud when adjusting the turnbuckle.