These are the solid boosters used in some Ariane 3 launches.
Available in 2 scales: the scale marked 1:128 is made for the Heller 1:125 Ariane 4 kit. 1:144 is for the Revell Ariane 4 kit.
Note: these are shorter than the boosters used for Ariane 4.
This part contains 2
You also need the attachment fittings, this part: https://www.shapeways.com/product/LKZ7T3E6U/ariane-4-pap-booster-attachment-fittings
For more information, see http://www.acme-engineering.nl/esa.html