Perimeter Markets Inc. is introducing a new three-tier minimum order policy for its BlockBook trading system.

Until now, it has imposed a one-size-fits-all minimum order size of 25,000 shares. “Our participants acknowledged that this was an imperfect solution — too large for less liquid symbols and too small for the low value, high volume symbols,” the company says. notes.

Effective October 2, Perimeter will expand its minimum order policy into three distinct tiers. Tier 1 will have a 50,000 share minimum; it includes Nortel, Bombardier and Abitibi. Tier 2 retains the 25,000 share minimum for S&P/TSX 60 names, excluding those in Tier 1. The minimum for Tier 3 will be 10,000 shares for all other names traded on BlockBook. Minimum order size for the “Follow-On Auction” remains unchanged at 100 shares.

“This is an important milestone in the evolution of BlockBook and shows the growing level of comfort of our users when managing their orders in our market,” it says. “Subscribers who wish to transact in larger sizes can still use the “Minimum Fill” or “All-or-None.” constraints during order entry to avoid smaller fills.”