Parker 51 Shell in Coco Michael Finlay but you can also try

but you can also try pushing the nib firmly into the bore in a disk to see which disk has a firmer fit

Size 14 x 2

The other type is the Snorkel tube with the flat front tip

On these newer 149s the slots are closer to 4:00 and 8:00

Parker 51 Shell in Coco Michael Finlay but you can also tryNew old stock. COCOA SHELLS HOODS FOR PARKER 51 Fountain Pens. Fine thread for standard size 51s. Won't fit the Demi. These are 48 threads per inch. These are available with and without cut outs for O Rings **Note: These will not fit Demi size 51s. **Note that Parker's Coco comes in a variety of shades, so the color may not match your barrel perfectly.