
Filet is a crochet technique where your stitches create a grid and either squares are filled in to create a design or the squares are left empty to create the pattern.
When using yarn you tend to leave gaps to create the design, but using thread you tend to fill in the grid to create the design.
I’ve kept the pattern simple for this, but you get the idea of how it works.
You can purchase the ad free, printable version of the pattern on Ravelry for just £2.40 which includes a weekly update with the next square
https://www.ravelry.com/patterns/library/the-50-stitches-cal
Filet designs are usually shown in a grid. The dark spaces are the gaps you leave by chaining 1 and skipping a stitch. The grid for this square is below

I have written out each row for you to follow as well.
UK translation
Double crochet = treble crochet
The Pattern
You will need a 3.5mm hook
Chain 32
Row 1. Dc in the 4th chain from your hook. Dc in each chain across (turning chain counts as a stitch) – 30 stitches total
Turn
Row 2. Alternate turning chain in first stitch, dc in next 5 stitches. Ch 1 (keep your tension loose when chaining), skip stitch dc in next 8 stitches. Ch1, skip stitch dc in next 8 stitches. Ch 1, skip stitch, dc in next 5 stitches

Row 3. Turning chain in first stitch, dc in next 5 stitches. Ch 1, skip stitch dc in next 8 stitches. Ch1, skip stitch dc in next 8 stitches. Ch 1, skip stitch, dc in next 5 stitches

Row 4. Turning chain in first stitch, dc in next 3 stitches. Ch 1, skip stitch dc in next 8 stitches. Ch1, skip stitch dc in next 8 stitches. Ch 1, skip stitch, dc in next 7 stitches
Row 5. Turning chain in first stitch, dc in next 7 stitches. Ch 1, skip stitch dc in next 8 stitches. Ch1, skip stitch dc in next 8 stitches. Ch 1, skip stitch, dc in next 3 stitches
Row 6. Turning chain in first stitch, dc in next stitch. Ch 1, skip stitch dc in next 8 stitches. Ch1, skip stitch dc in next 8 stitches. Ch 1, skip stitch, dc in next 9 stitches
Row 7. Turning chain in first stitch, Ch 1, skip stitch dc in next 8 stitches. Ch1, skip stitch dc in next 8 stitches. Ch 1, skip stitch, dc in next 8 stitches. Ch 1, skip stitch, dc in next stitch
Row 8. Turning chain in first stitch, dc in next 8 stitches. Ch 1, skip stitch dc in next 8 stitches. Ch1, skip stitch dc in next 8 stitches. Ch 1, skip stitch, dc in next 2 stitches
Row 9. Turning chain in first stitch, dc in next 2 stitches. Ch 1, skip stitch dc in next 8 stitches. Ch1, skip stitch dc in next 8 stitches. Ch 1, skip stitch, dc in next 8 stitches
Row 10 Turning chain in first stitch, dc in next 6 stitches. Ch 1, skip stitch dc in next 8 stitches. Ch1, skip stitch dc in next 8 stitches. Ch 1, skip stitch, dc in next 4 stitches
Row 11. Turning chain in first stitch, dc in next 4 stitches. Ch 1, skip stitch dc in next 8 stitches. Ch1, skip stitch dc in next 8 stitches. Ch 1, skip stitch, dc in next 6 stitches
Row 12. Turning chain in first stitch, dc in next 4 stitches. Ch 1, skip stitch dc in next 8 stitches. Ch1, skip stitch dc in next 8 stitches. Ch 1, skip stitch, dc in next 6 stitches
Row 13. Turning chain in first stitch, dc in each stitch across
The Border
Sc in each stitch along the top and bottom. Make 3 sc in the side of rows 1, 4, 10 and 13. Make 2 sc in the side of every other row. Add an extra sc in the corners for the turn – 124 sc total
The Interlocking Border
If you are joining as you go, we need to add the interlocking border and weave it into the border of the previous square so they are joined together. Use a 4mm hook for this part of the border on all squares.
Start the border in the extra corner stitch on the bottom left hand side with a standing single crochet, and single crochet in the next corner stitch.
*Chain 4, skip the next 3 stitches, single crochet in the next two stitches* repeat this pattern across the bottom edge until you reach the next corner (you should have 6 loops). Make a single crochet in all 3 corner stitches. Carry on the pattern above. Do this for 3 sides.
When you get to the top left corner, single crochet in the 3 corner stitches then chain 4. Pull up a loop, then insert your hook into the top right loop of the previous square. Hook the loop from your chain 4 and pull it up through the seed stitch loop. Pull your loop tight, skip 3 and single crochet in the next 2 stitches of the adjoining square.
You should have joined the first 2 loops together. Repeat this for all 6 loops until you get back to the bottom left hand corner. Single crochet in the corner stitch, and join into the standing stitch.
You can now tie off and weave in your ends.
If you have any questions about the pattern or the CAL, then come on over to the Facebook group – 50 Stitches where you can show us your completed squares too.