The Silver Viscount 721D overlocker is a lightweight 3 or 4 thread overlocking machine with a built-in tension adjusting device, differential feed and stitch length adjustment (1.1-4.0 mm) functions, automatic looper threader, built-in rolled hem, upper knife clutch device and a detachable extension plate for free arm sewing.
The 721d model is a improved version of the popular, but now discontinued 720d.
It has a variable stitch width of 2.3 - 7.0mm and an automatic safety switch which is activated when the looper cover is opened. Threading is quicker than most machines, thanks to colour-coded threading paths to follow, the bright LED lighting up the sewing bed and a self-threading lower looper. Simply lay the thread into the guide, flick a switch and the lower looper is threaded. The guide is automatically returned to its normal position when you turn the balance wheel.
The Silver 721D is a very versitile overlocker that can stitch at great speeds of up to 1300 spm. It is a true stitching performer, thanks to the built-in tensions, looper threading and sleeve arm when needed.
When lifting the presser foot for re-threading, the thread tensions are automatically released at the touch of a button so you can draw the thread smoothly.
An optional pack of snap-on feet is available which includes an elastic foot, blind hem/lace foot, gathering foot, pearl/sequence foot and a piping foot. 
This overlocker has many functions and is a very reliable, affordable and popular model.