Lash-line hardware

Lash-line hardware is an ancient (dating to at least the 1920s) form of temporarily joining flatwork when a scene must be set-up and struck quickly. A lash-line is typically 1/4" Cotton sash cord, attached to the top stile of the left flat via a lash line eye.

Week 2

Older methods had the lashline tied through a hole drilled in the corner block.

The lashline then zig-zags around alternating lashline cleats.
Several different types shown:

Week 2

Lashing Cleats / Lashing Hardware / Theatrical & Set Hardware / Home - Mutual Hardware

Round Line Cleat / Lashing Hardware / Theatrical & Set Hardware / Home - Mutual Hardware

Offset Round Line Cleat / Lashing Hardware / Theatrical & Set Hardware / Home - Mutual Hardware

Installing Flats

From http://www.ia470.com/primer/scenery.htm:

Traditional approach, somewhat uncommon now: specialized stage hardware used with #8 cotton sash cord to lash flats together.
Requires lash hardware:

Lash eyes- these are placed on the top left hand flat as you face the back of seam. They go on this side because most people are right handed. The sash cord passes through the eye and knotted with an overhand or figure-eight knot.

Lash cleats- spaced alternately down the flat joint, these are designed so the rope can slide over them when you pull them tight.

Tie-off cleat - this is designed so the rope doesn't slide when you pull it tight.

Stop cleat- These are placed to prevent the flats from sliding past each other when a corner is made.

To use, the flats are butted together, and the rope is flipped alternately around the lash cleats, then tied off over the stop cleat with a lash line tie-off knot that holds under pressure, but which can be quickly released to shift.