Practice Jacks are exactly the same size/weight as Standard (Match) Jacks and have the same bias, the only difference is that they do not have a BCGBA stamp.
Normally Standard/Match Jacks cost at least £10 more than Practice Jacks, so it makes sense for bowlers to buy the cheaper version. Standard/Match Jacks are normally purchased by Clubs, but some bowlers prefer to purchase them instead of Practice Jacks (for some reason). Practice Jacks can be any colour one chooses (subject to availability), and are sometimes sold as pairs for children to use as bowls. A tip from us is to buy an obscure colour, to enable easy identification.
The game shall be played with standard jacks of 2 full bias as approved by the British Crown Green Bowling Association. Jacks manufactured after 1st March 2004 shall be black or yellow in colour. They shall weigh 666grams plus or minus 10grams. The width shall be 90.5mm plus or minus 0.5mm. The height shall be 98mm plus or minus 0.5mm.